First commitHEADmaster

47 files changed, 2242 insertions, 0 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..648f8b2
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,61 @@
+# wip, a small TCP/IP stack.
+# Copyright (C) 2025  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+cmake_minimum_required(VERSION 3.19)
+project(wip LANGUAGES C VERSION 0.0.0)
+option(WIP_LOG "Enables logging to stderr")
+option(WIP_LOG_CUSTOM "Allows user code to define wip_log. Enables WIP_LOG")
+add_library(${PROJECT_NAME})
+target_include_directories(${PROJECT_NAME} PUBLIC include
+    PRIVATE private_include)
+
+set(compilers
+    "GNU"
+    "Clang"
+    "TinyCC"
+)
+
+if(WIP_LOG_CUSTOM)
+    set(WIP_LOG ON)
+endif()
+
+foreach(c ${compilers})
+    if(CMAKE_C_COMPILER_ID STREQUAL ${c})
+        set(cflags_np
+            -pedantic
+            -Wall
+        )
+
+        if(CMAKE_BUILD_TYPE STREQUAL "Debug")
+            set(cflags_np ${cflags_np} -Og -g)
+        else()
+            set(cflags_np ${cflags_np} -Os)
+        endif()
+
+        break()
+    endif()
+endforeach()
+
+include(CheckCompilerFlag)
+
+foreach(f ${cflags_np})
+    string(REPLACE "-" "_" var supported_${f})
+    check_compiler_flag(C ${f} ${var})
+
+    if(${var})
+        set(sup_cflags ${sup_cflags} ${f})
+    endif()
+endforeach()
+
+if(WIP_LOG)
+    target_compile_definitions(${PROJECT_NAME} PRIVATE WIP_LOG)
+endif()
+
+target_compile_options(${PROJECT_NAME} PRIVATE ${sup_cflags})
+set_target_properties(${PROJECT_NAME} PROPERTIES C_STANDARD 90 C_EXTENSIONS OFF)
+add_subdirectory(src)
+install(TARGETS ${PROJECT_NAME})
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..d0a1fa1
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,373 @@
+Mozilla Public License Version 2.0
+==================================
+
+1. Definitions
+--------------
+
+1.1. "Contributor"
+    means each individual or legal entity that creates, contributes to
+    the creation of, or owns Covered Software.
+
+1.2. "Contributor Version"
+    means the combination of the Contributions of others (if any) used
+    by a Contributor and that particular Contributor's Contribution.
+
+1.3. "Contribution"
+    means Covered Software of a particular Contributor.
+
+1.4. "Covered Software"
+    means Source Code Form to which the initial Contributor has attached
+    the notice in Exhibit A, the Executable Form of such Source Code
+    Form, and Modifications of such Source Code Form, in each case
+    including portions thereof.
+
+1.5. "Incompatible With Secondary Licenses"
+    means
+
+    (a) that the initial Contributor has attached the notice described
+        in Exhibit B to the Covered Software; or
+
+    (b) that the Covered Software was made available under the terms of
+        version 1.1 or earlier of the License, but not also under the
+        terms of a Secondary License.
+
+1.6. "Executable Form"
+    means any form of the work other than Source Code Form.
+
+1.7. "Larger Work"
+    means a work that combines Covered Software with other material, in
+    a separate file or files, that is not Covered Software.
+
+1.8. "License"
+    means this document.
+
+1.9. "Licensable"
+    means having the right to grant, to the maximum extent possible,
+    whether at the time of the initial grant or subsequently, any and
+    all of the rights conveyed by this License.
+
+1.10. "Modifications"
+    means any of the following:
+
+    (a) any file in Source Code Form that results from an addition to,
+        deletion from, or modification of the contents of Covered
+        Software; or
+
+    (b) any new file in Source Code Form that contains any Covered
+        Software.
+
+1.11. "Patent Claims" of a Contributor
+    means any patent claim(s), including without limitation, method,
+    process, and apparatus claims, in any patent Licensable by such
+    Contributor that would be infringed, but for the grant of the
+    License, by the making, using, selling, offering for sale, having
+    made, import, or transfer of either its Contributions or its
+    Contributor Version.
+
+1.12. "Secondary License"
+    means either the GNU General Public License, Version 2.0, the GNU
+    Lesser General Public License, Version 2.1, the GNU Affero General
+    Public License, Version 3.0, or any later versions of those
+    licenses.
+
+1.13. "Source Code Form"
+    means the form of the work preferred for making modifications.
+
+1.14. "You" (or "Your")
+    means an individual or a legal entity exercising rights under this
+    License. For legal entities, "You" includes any entity that
+    controls, is controlled by, or is under common control with You. For
+    purposes of this definition, "control" means (a) the power, direct
+    or indirect, to cause the direction or management of such entity,
+    whether by contract or otherwise, or (b) ownership of more than
+    fifty percent (50%) of the outstanding shares or beneficial
+    ownership of such entity.
+
+2. License Grants and Conditions
+--------------------------------
+
+2.1. Grants
+
+Each Contributor hereby grants You a world-wide, royalty-free,
+non-exclusive license:
+
+(a) under intellectual property rights (other than patent or trademark)
+    Licensable by such Contributor to use, reproduce, make available,
+    modify, display, perform, distribute, and otherwise exploit its
+    Contributions, either on an unmodified basis, with Modifications, or
+    as part of a Larger Work; and
+
+(b) under Patent Claims of such Contributor to make, use, sell, offer
+    for sale, have made, import, and otherwise transfer either its
+    Contributions or its Contributor Version.
+
+2.2. Effective Date
+
+The licenses granted in Section 2.1 with respect to any Contribution
+become effective for each Contribution on the date the Contributor first
+distributes such Contribution.
+
+2.3. Limitations on Grant Scope
+
+The licenses granted in this Section 2 are the only rights granted under
+this License. No additional rights or licenses will be implied from the
+distribution or licensing of Covered Software under this License.
+Notwithstanding Section 2.1(b) above, no patent license is granted by a
+Contributor:
+
+(a) for any code that a Contributor has removed from Covered Software;
+    or
+
+(b) for infringements caused by: (i) Your and any other third party's
+    modifications of Covered Software, or (ii) the combination of its
+    Contributions with other software (except as part of its Contributor
+    Version); or
+
+(c) under Patent Claims infringed by Covered Software in the absence of
+    its Contributions.
+
+This License does not grant any rights in the trademarks, service marks,
+or logos of any Contributor (except as may be necessary to comply with
+the notice requirements in Section 3.4).
+
+2.4. Subsequent Licenses
+
+No Contributor makes additional grants as a result of Your choice to
+distribute the Covered Software under a subsequent version of this
+License (see Section 10.2) or under the terms of a Secondary License (if
+permitted under the terms of Section 3.3).
+
+2.5. Representation
+
+Each Contributor represents that the Contributor believes its
+Contributions are its original creation(s) or it has sufficient rights
+to grant the rights to its Contributions conveyed by this License.
+
+2.6. Fair Use
+
+This License is not intended to limit any rights You have under
+applicable copyright doctrines of fair use, fair dealing, or other
+equivalents.
+
+2.7. Conditions
+
+Sections 3.1, 3.2, 3.3, and 3.4 are conditions of the licenses granted
+in Section 2.1.
+
+3. Responsibilities
+-------------------
+
+3.1. Distribution of Source Form
+
+All distribution of Covered Software in Source Code Form, including any
+Modifications that You create or to which You contribute, must be under
+the terms of this License. You must inform recipients that the Source
+Code Form of the Covered Software is governed by the terms of this
+License, and how they can obtain a copy of this License. You may not
+attempt to alter or restrict the recipients' rights in the Source Code
+Form.
+
+3.2. Distribution of Executable Form
+
+If You distribute Covered Software in Executable Form then:
+
+(a) such Covered Software must also be made available in Source Code
+    Form, as described in Section 3.1, and You must inform recipients of
+    the Executable Form how they can obtain a copy of such Source Code
+    Form by reasonable means in a timely manner, at a charge no more
+    than the cost of distribution to the recipient; and
+
+(b) You may distribute such Executable Form under the terms of this
+    License, or sublicense it under different terms, provided that the
+    license for the Executable Form does not attempt to limit or alter
+    the recipients' rights in the Source Code Form under this License.
+
+3.3. Distribution of a Larger Work
+
+You may create and distribute a Larger Work under terms of Your choice,
+provided that You also comply with the requirements of this License for
+the Covered Software. If the Larger Work is a combination of Covered
+Software with a work governed by one or more Secondary Licenses, and the
+Covered Software is not Incompatible With Secondary Licenses, this
+License permits You to additionally distribute such Covered Software
+under the terms of such Secondary License(s), so that the recipient of
+the Larger Work may, at their option, further distribute the Covered
+Software under the terms of either this License or such Secondary
+License(s).
+
+3.4. Notices
+
+You may not remove or alter the substance of any license notices
+(including copyright notices, patent notices, disclaimers of warranty,
+or limitations of liability) contained within the Source Code Form of
+the Covered Software, except that You may alter any license notices to
+the extent required to remedy known factual inaccuracies.
+
+3.5. Application of Additional Terms
+
+You may choose to offer, and to charge a fee for, warranty, support,
+indemnity or liability obligations to one or more recipients of Covered
+Software. However, You may do so only on Your own behalf, and not on
+behalf of any Contributor. You must make it absolutely clear that any
+such warranty, support, indemnity, or liability obligation is offered by
+You alone, and You hereby agree to indemnify every Contributor for any
+liability incurred by such Contributor as a result of warranty, support,
+indemnity or liability terms You offer. You may include additional
+disclaimers of warranty and limitations of liability specific to any
+jurisdiction.
+
+4. Inability to Comply Due to Statute or Regulation
+---------------------------------------------------
+
+If it is impossible for You to comply with any of the terms of this
+License with respect to some or all of the Covered Software due to
+statute, judicial order, or regulation then You must: (a) comply with
+the terms of this License to the maximum extent possible; and (b)
+describe the limitations and the code they affect. Such description must
+be placed in a text file included with all distributions of the Covered
+Software under this License. Except to the extent prohibited by statute
+or regulation, such description must be sufficiently detailed for a
+recipient of ordinary skill to be able to understand it.
+
+5. Termination
+--------------
+
+5.1. The rights granted under this License will terminate automatically
+if You fail to comply with any of its terms. However, if You become
+compliant, then the rights granted under this License from a particular
+Contributor are reinstated (a) provisionally, unless and until such
+Contributor explicitly and finally terminates Your grants, and (b) on an
+ongoing basis, if such Contributor fails to notify You of the
+non-compliance by some reasonable means prior to 60 days after You have
+come back into compliance. Moreover, Your grants from a particular
+Contributor are reinstated on an ongoing basis if such Contributor
+notifies You of the non-compliance by some reasonable means, this is the
+first time You have received notice of non-compliance with this License
+from such Contributor, and You become compliant prior to 30 days after
+Your receipt of the notice.
+
+5.2. If You initiate litigation against any entity by asserting a patent
+infringement claim (excluding declaratory judgment actions,
+counter-claims, and cross-claims) alleging that a Contributor Version
+directly or indirectly infringes any patent, then the rights granted to
+You by any and all Contributors for the Covered Software under Section
+2.1 of this License shall terminate.
+
+5.3. In the event of termination under Sections 5.1 or 5.2 above, all
+end user license agreements (excluding distributors and resellers) which
+have been validly granted by You or Your distributors under this License
+prior to termination shall survive termination.
+
+************************************************************************
+*                                                                      *
+*  6. Disclaimer of Warranty                                           *
+*  -------------------------                                           *
+*                                                                      *
+*  Covered Software is provided under this License on an "as is"       *
+*  basis, without warranty of any kind, either expressed, implied, or  *
+*  statutory, including, without limitation, warranties that the       *
+*  Covered Software is free of defects, merchantable, fit for a        *
+*  particular purpose or non-infringing. The entire risk as to the     *
+*  quality and performance of the Covered Software is with You.        *
+*  Should any Covered Software prove defective in any respect, You     *
+*  (not any Contributor) assume the cost of any necessary servicing,   *
+*  repair, or correction. This disclaimer of warranty constitutes an   *
+*  essential part of this License. No use of any Covered Software is   *
+*  authorized under this License except under this disclaimer.         *
+*                                                                      *
+************************************************************************
+
+************************************************************************
+*                                                                      *
+*  7. Limitation of Liability                                          *
+*  --------------------------                                          *
+*                                                                      *
+*  Under no circumstances and under no legal theory, whether tort      *
+*  (including negligence), contract, or otherwise, shall any           *
+*  Contributor, or anyone who distributes Covered Software as          *
+*  permitted above, be liable to You for any direct, indirect,         *
+*  special, incidental, or consequential damages of any character      *
+*  including, without limitation, damages for lost profits, loss of    *
+*  goodwill, work stoppage, computer failure or malfunction, or any    *
+*  and all other commercial damages or losses, even if such party      *
+*  shall have been informed of the possibility of such damages. This   *
+*  limitation of liability shall not apply to liability for death or   *
+*  personal injury resulting from such party's negligence to the       *
+*  extent applicable law prohibits such limitation. Some               *
+*  jurisdictions do not allow the exclusion or limitation of           *
+*  incidental or consequential damages, so this exclusion and          *
+*  limitation may not apply to You.                                    *
+*                                                                      *
+************************************************************************
+
+8. Litigation
+-------------
+
+Any litigation relating to this License may be brought only in the
+courts of a jurisdiction where the defendant maintains its principal
+place of business and such litigation shall be governed by laws of that
+jurisdiction, without reference to its conflict-of-law provisions.
+Nothing in this Section shall prevent a party's ability to bring
+cross-claims or counter-claims.
+
+9. Miscellaneous
+----------------
+
+This License represents the complete agreement concerning the subject
+matter hereof. If any provision of this License is held to be
+unenforceable, such provision shall be reformed only to the extent
+necessary to make it enforceable. Any law or regulation which provides
+that the language of a contract shall be construed against the drafter
+shall not be used to construe this License against a Contributor.
+
+10. Versions of the License
+---------------------------
+
+10.1. New Versions
+
+Mozilla Foundation is the license steward. Except as provided in Section
+10.3, no one other than the license steward has the right to modify or
+publish new versions of this License. Each version will be given a
+distinguishing version number.
+
+10.2. Effect of New Versions
+
+You may distribute the Covered Software under the terms of the version
+of the License under which You originally received the Covered Software,
+or under the terms of any subsequent version published by the license
+steward.
+
+10.3. Modified Versions
+
+If you create software not governed by this License, and you want to
+create a new license for such software, you may create and use a
+modified version of this License if you rename the license and remove
+any references to the name of the license steward (except to note that
+such modified license differs from this License).
+
+10.4. Distributing Source Code Form that is Incompatible With Secondary
+Licenses
+
+If You choose to distribute Source Code Form that is Incompatible With
+Secondary Licenses under the terms of this version of the License, the
+notice described in Exhibit B of this License must be attached.
+
+Exhibit A - Source Code Form License Notice
+-------------------------------------------
+
+  This Source Code Form is subject to the terms of the Mozilla Public
+  License, v. 2.0. If a copy of the MPL was not distributed with this
+  file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+If it is not possible or desirable to put the notice in a particular
+file, then You may include the notice in a location (such as a LICENSE
+file in a relevant directory) where a recipient would be likely to look
+for such a notice.
+
+You may add additional accurate notices of copyright ownership.
+
+Exhibit B - "Incompatible With Secondary Licenses" Notice
+---------------------------------------------------------
+
+  This Source Code Form is "Incompatible With Secondary Licenses", as
+  defined by the Mozilla Public License, v. 2.0.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..e177223
--- /dev/null
+++ b/README.md
@@ -0,0 +1,18 @@
+# wip
+
+**This project is still unfinished and is not meant for production use.**
+
+`wip` (prounced _weep_ or _double u-ip_) is a small TCP/IP stack.
+
+## License
+
+```
+wip, a small TCP/IP stack.
+Copyright (C) 2025  Xavier Del Campo Romero
+
+This Source Code Form is subject to the terms of the Mozilla Public
+License, v. 2.0. If a copy of the MPL was not distributed with this
+file, You can obtain one at https://mozilla.org/MPL/2.0/.
+```
+
+Also, see [`LICENSE`](LICENSE).
diff --git a/include/wip/private.h b/include/wip/private.h
new file mode 100644
index 0000000..6de3733
--- /dev/null
+++ b/include/wip/private.h
@@ -0,0 +1,96 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef WIP_PRIVATE_H
+#define WIP_PRIVATE_H
+
+#include <stddef.h>
+
+#if !defined(WIP_H) && !defined(WIP_TYPES_H)
+#error Do not #include <wip/private.h> directly. \
+    Please either #include <wip/wip.h> or <wip/types.h>
+#endif
+
+struct wip;
+
+typedef void *(*wip_prot_alloc)(struct wip *);
+typedef enum wip_state (*wip_prot_rx)(struct wip *, const void *, size_t, void *);
+typedef int (*wip_prot_tx)(struct wip *, void *, size_t, void *);
+typedef void (*wip_prot_free)(struct wip *, void *);
+
+enum wip_protocol
+{
+    WIP_P_ICMP = 1,
+    WIP_P_IGMP,
+    WIP_P_TCP = 6,
+    WIP_P_UDP = 17
+};
+
+struct wip_prot_ops
+{
+    unsigned char id;
+    wip_prot_alloc alloc;
+    wip_prot_free free;
+    wip_prot_rx rx;
+    wip_prot_tx tx;
+};
+
+struct wip_sm_io
+{
+    void *buf;
+    size_t n, read;
+};
+
+struct wip_be16
+{
+    unsigned char v[2];
+};
+
+struct wip_be32
+{
+    unsigned char v[4];
+};
+
+union wip_rx_sm
+{
+    struct wip_rx_sm_h
+    {
+        unsigned short chksum;
+        unsigned char ttl, protocol;
+        size_t header_sz, i;
+        struct wip_sm_io io;
+        struct wip_be16 len, id, fl_off, rchksum;
+        struct wip_be32 src, dst;
+        const struct wip_prot_ops *prot;
+        void *args;
+    } h;
+};
+
+struct wip_rx
+{
+    char buf[192];
+    union wip_rx_sm sm;
+    enum wip_state (*next)(struct wip *);
+};
+
+struct wip_tx
+{
+    char buf[192];
+    enum wip_state (*next)(struct wip *);
+};
+
+struct wip
+{
+    const char *exception;
+    struct wip_rx rx;
+    struct wip_tx tx;
+    struct wip_cfg cfg;
+};
+
+#endif
diff --git a/include/wip/types.h b/include/wip/types.h
new file mode 100644
index 0000000..b97f7b9
--- /dev/null
+++ b/include/wip/types.h
@@ -0,0 +1,44 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef WIP_TYPES_H
+#define WIP_TYPES_H
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+enum wip_state
+{
+    WIP_OK,
+    WIP_AGAIN,
+    WIP_INVALID,
+    WIP_FATAL
+};
+
+struct wip_cfg
+{
+    void *(*alloc)(size_t n, void *user);
+    void *(*realloc)(void *p, size_t n, void *user);
+    void (*free)(void *p, void *user);
+    int (*read)(void *buf, size_t n, void *user);
+    int (*write)(const void *buf, size_t n, void *user);
+    void *user;
+};
+
+#include <wip/private.h>
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/include/wip/wip.h b/include/wip/wip.h
new file mode 100644
index 0000000..22c9f8c
--- /dev/null
+++ b/include/wip/wip.h
@@ -0,0 +1,28 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef WIP_H
+#define WIP_H
+
+#include <wip/types.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+void wip_init(struct wip *w, const struct wip_cfg *cfg);
+int wip_run(struct wip *w);
+const char *wip_exc(const struct wip *w);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/private_include/wip/prv/icmp.h b/private_include/wip/prv/icmp.h
new file mode 100644
index 0000000..bc7dbe1
--- /dev/null
+++ b/private_include/wip/prv/icmp.h
@@ -0,0 +1,21 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef WIP_PRV_ICMP_H
+#define WIP_PRV_ICMP_H
+
+#include <wip/wip.h>
+#include <stddef.h>
+
+void *wip_icmp_alloc(struct wip *const w);
+enum wip_state wip_icmp_rx(struct wip *w, const void *buf, size_t n, void *args);
+int wip_icmp_tx(struct wip *w, void *buf, size_t n, void *args);
+void wip_icmp_free(struct wip *w, void *args);
+
+#endif
diff --git a/private_include/wip/prv/icmp/routines.h b/private_include/wip/prv/icmp/routines.h
new file mode 100644
index 0000000..508efce
--- /dev/null
+++ b/private_include/wip/prv/icmp/routines.h
@@ -0,0 +1,20 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef WIP_PRV_ICMP_ROUTINES_H
+#define WIP_PRV_ICMP_ROUTINES_H
+
+#include <wip/wip.h>
+#include <wip/prv/icmp/types.h>
+#include <stddef.h>
+
+enum wip_state wip_icmp_rx_start(struct wip *w, const void *buf, size_t n,
+    struct wip_icmp *icmp, size_t *r);
+
+#endif
diff --git a/private_include/wip/prv/icmp/types.h b/private_include/wip/prv/icmp/types.h
new file mode 100644
index 0000000..c9355dd
--- /dev/null
+++ b/private_include/wip/prv/icmp/types.h
@@ -0,0 +1,34 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef WIP_PRV_ICMP_TYPES_H
+#define WIP_PRV_ICMP_TYPES_H
+
+#include <wip/wip.h>
+#include <stddef.h>
+
+enum icmp_type
+{
+    ICMP_ECHO_REPLY,
+    ICMP_ECHO_REQUEST = 8
+};
+
+struct wip_icmp
+{
+    enum icmp_type type;
+    struct wip_sm_io io;
+    struct wip_be16 exp_checksum, id, seqnum;
+    unsigned short checksum;
+    void *buf;
+    size_t read;
+    enum wip_state (*next)(struct wip *, const void *, size_t,
+        struct wip_icmp *, size_t *);
+};
+
+#endif
diff --git a/private_include/wip/prv/io.h b/private_include/wip/prv/io.h
new file mode 100644
index 0000000..cece6b3
--- /dev/null
+++ b/private_include/wip/prv/io.h
@@ -0,0 +1,22 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef WIP_IO_H
+#define WIP_IO_H
+
+#include <wip/wip.h>
+
+enum wip_state wip_io_read(struct wip *w, struct wip_sm_io *io);
+enum wip_state wip_io_read_c(struct wip_cfg *cfg, struct wip_sm_io *io);
+unsigned short wip_be16(const struct wip_be16 *v);
+unsigned long wip_be32(const struct wip_be32 *v);
+void wip_tobe16(unsigned long v, struct wip_be16 *out);
+void wip_tobe32(unsigned long v, struct wip_be32 *out);
+
+#endif
diff --git a/private_include/wip/prv/log.h b/private_include/wip/prv/log.h
new file mode 100644
index 0000000..438b569
--- /dev/null
+++ b/private_include/wip/prv/log.h
@@ -0,0 +1,15 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef WIP_LOG_H
+#define WIP_LOG_H
+
+int wip_log(const char *fmt, ...);
+
+#endif
diff --git a/private_include/wip/prv/routines.h b/private_include/wip/prv/routines.h
new file mode 100644
index 0000000..e8e919b
--- /dev/null
+++ b/private_include/wip/prv/routines.h
@@ -0,0 +1,17 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef WIP_PRV_ROUTINES_H
+#define WIP_PRV_ROUTINES_H
+
+#include <wip/wip.h>
+
+void wip_rx(struct wip *w);
+
+#endif
diff --git a/private_include/wip/prv/tcp.h b/private_include/wip/prv/tcp.h
new file mode 100644
index 0000000..8919ba2
--- /dev/null
+++ b/private_include/wip/prv/tcp.h
@@ -0,0 +1,21 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef WIP_PRV_TCP_H
+#define WIP_PRV_TCP_H
+
+#include <wip/wip.h>
+#include <stddef.h>
+
+void *wip_tcp_alloc(struct wip *const w);
+enum wip_state wip_tcp_rx(struct wip *w, const void *buf, size_t n, void *args);
+int wip_tcp_tx(struct wip *w, void *buf, size_t n, void *args);
+void wip_tcp_free(struct wip *w, void *args);
+
+#endif
diff --git a/private_include/wip/prv/tcp/types.h b/private_include/wip/prv/tcp/types.h
new file mode 100644
index 0000000..66dfdb4
--- /dev/null
+++ b/private_include/wip/prv/tcp/types.h
@@ -0,0 +1,20 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef WIP_PRV_TCP_TYPES_H
+#define WIP_PRV_TCP_TYPES_H
+
+#include <stddef.h>
+
+struct wip_tcp
+{
+    int dummy;
+};
+
+#endif
diff --git a/private_include/wip/prv/udp.h b/private_include/wip/prv/udp.h
new file mode 100644
index 0000000..48422fe
--- /dev/null
+++ b/private_include/wip/prv/udp.h
@@ -0,0 +1,21 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef WIP_PRV_UDP_H
+#define WIP_PRV_UDP_H
+
+#include <wip/wip.h>
+#include <stddef.h>
+
+void *wip_udp_alloc(struct wip *const w);
+enum wip_state wip_udp_rx(struct wip *w, const void *buf, size_t n, void *args);
+int wip_udp_tx(struct wip *w, void *buf, size_t n, void *args);
+void wip_udp_free(struct wip *w, void *args);
+
+#endif
diff --git a/private_include/wip/prv/udp/types.h b/private_include/wip/prv/udp/types.h
new file mode 100644
index 0000000..c807430
--- /dev/null
+++ b/private_include/wip/prv/udp/types.h
@@ -0,0 +1,20 @@
+/*
+ * wip, a small UDP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef WIP_PRV_UDP_TYPES_H
+#define WIP_PRV_UDP_TYPES_H
+
+#include <stddef.h>
+
+struct wip_udp
+{
+    int dummy;
+};
+
+#endif
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
new file mode 100644
index 0000000..8ca9376
--- /dev/null
+++ b/src/CMakeLists.txt
@@ -0,0 +1,16 @@
+# wip, a small TCP/IP stack.
+# Copyright (C) 2025  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+target_sources(${PROJECT_NAME} PRIVATE
+    init.c
+    run.c
+)
+
+add_subdirectory(io)
+add_subdirectory(log)
+add_subdirectory(protocol)
+add_subdirectory(routines)
diff --git a/src/init.c b/src/init.c
new file mode 100644
index 0000000..570f78b
--- /dev/null
+++ b/src/init.c
@@ -0,0 +1,20 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/routines.h>
+
+void wip_init(struct wip *const w, const struct wip_cfg *const cfg)
+{
+    const struct wip ww = {0};
+
+    *w = ww;
+    w->cfg = *cfg;
+    wip_rx(w);
+}
diff --git a/src/io/CMakeLists.txt b/src/io/CMakeLists.txt
new file mode 100644
index 0000000..b989afd
--- /dev/null
+++ b/src/io/CMakeLists.txt
@@ -0,0 +1,15 @@
+# wip, a small TCP/IP stack.
+# Copyright (C) 2025  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+target_sources(${PROJECT_NAME} PRIVATE
+    be16.c
+    be32.c
+    read.c
+    read_c.c
+    tobe16.c
+    tobe32.c
+)
diff --git a/src/io/be16.c b/src/io/be16.c
new file mode 100644
index 0000000..d8b995a
--- /dev/null
+++ b/src/io/be16.c
@@ -0,0 +1,16 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/io.h>
+
+unsigned short wip_be16(const struct wip_be16 *const v)
+{
+    return ((unsigned long)v->v[0] << 8) | v->v[1];
+}
diff --git a/src/io/be32.c b/src/io/be32.c
new file mode 100644
index 0000000..9defd06
--- /dev/null
+++ b/src/io/be32.c
@@ -0,0 +1,17 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/io.h>
+
+unsigned long wip_be32(const struct wip_be32 *const v)
+{
+    return ((unsigned long)v->v[0] << 24) | ((unsigned long)v->v[1] << 16)
+        | (v->v[2] << 8) | v->v[3];
+}
diff --git a/src/io/read.c b/src/io/read.c
new file mode 100644
index 0000000..f8ee1b2
--- /dev/null
+++ b/src/io/read.c
@@ -0,0 +1,32 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/io.h>
+
+enum wip_state wip_io_read(struct wip *const w, struct wip_sm_io *const io)
+{
+    void *const buf = (unsigned char *)io->buf + io->read;
+    const struct wip_cfg *const cfg = &w->cfg;
+    const size_t rem = io->n - io->read;
+    const int n = cfg->read(buf, rem, cfg->user);
+
+    if (n < 0)
+    {
+        w->exception = "read error";
+        return WIP_FATAL;
+    }
+    else if ((io->read += n) >= io->n)
+    {
+        io->read = 0;
+        return WIP_OK;
+    }
+
+    return WIP_AGAIN;
+}
diff --git a/src/io/read_c.c b/src/io/read_c.c
new file mode 100644
index 0000000..4433a9f
--- /dev/null
+++ b/src/io/read_c.c
@@ -0,0 +1,28 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/io.h>
+
+enum wip_state wip_io_read_c(struct wip_cfg *const cfg, struct wip_sm_io *const io)
+{
+    void *const buf = (unsigned char *)io->buf + io->read;
+    const size_t rem = io->n - io->read;
+    const int n = cfg->read(buf, rem, cfg->user);
+
+    if (n < 0)
+        return WIP_FATAL;
+    else if ((io->read += n) >= io->n)
+    {
+        io->read = 0;
+        return WIP_OK;
+    }
+
+    return WIP_AGAIN;
+}
diff --git a/src/io/tobe16.c b/src/io/tobe16.c
new file mode 100644
index 0000000..3ac7992
--- /dev/null
+++ b/src/io/tobe16.c
@@ -0,0 +1,17 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/io.h>
+
+void wip_tobe16(const unsigned long v, struct wip_be16 *const r)
+{
+    r->v[0] = v >> 8;
+    r->v[1] = v;
+}
diff --git a/src/io/tobe32.c b/src/io/tobe32.c
new file mode 100644
index 0000000..251a0f9
--- /dev/null
+++ b/src/io/tobe32.c
@@ -0,0 +1,19 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/io.h>
+
+void wip_tobe32(const unsigned long v, struct wip_be32 *const r)
+{
+    r->v[0] = v >> 24;
+    r->v[1] = v >> 16;
+    r->v[2] = v >> 8;
+    r->v[3] = v;
+}
diff --git a/src/log/CMakeLists.txt b/src/log/CMakeLists.txt
new file mode 100644
index 0000000..e4a0289
--- /dev/null
+++ b/src/log/CMakeLists.txt
@@ -0,0 +1,10 @@
+# wip, a small TCP/IP stack.
+# Copyright (C) 2025  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+if(WIP_LOG AND NOT WIP_LOG_CUSTOM)
+    target_sources(${PROJECT_NAME} PRIVATE log.c)
+endif()
diff --git a/src/log/log.c b/src/log/log.c
new file mode 100644
index 0000000..b9e20af
--- /dev/null
+++ b/src/log/log.c
@@ -0,0 +1,23 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/prv/log.h>
+#include <stdarg.h>
+#include <stdio.h>
+
+int nwp_log(const char *const fmt, ...)
+{
+    va_list ap;
+    int ret;
+
+    va_start(ap, fmt);
+    ret = vfprintf(stderr, fmt, ap);
+    va_end(ap);
+    return ret;
+}
diff --git a/src/protocol/CMakeLists.txt b/src/protocol/CMakeLists.txt
new file mode 100644
index 0000000..194274d
--- /dev/null
+++ b/src/protocol/CMakeLists.txt
@@ -0,0 +1,10 @@
+# wip, a small TCP/IP stack.
+# Copyright (C) 2025  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+add_subdirectory(icmp)
+add_subdirectory(tcp)
+add_subdirectory(udp)
diff --git a/src/protocol/icmp/CMakeLists.txt b/src/protocol/icmp/CMakeLists.txt
new file mode 100644
index 0000000..4fd374d
--- /dev/null
+++ b/src/protocol/icmp/CMakeLists.txt
@@ -0,0 +1,14 @@
+# wip, a small TCP/IP stack.
+# Copyright (C) 2025  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+target_sources(${PROJECT_NAME} PRIVATE
+    alloc.c
+    free.c
+    rx.c
+    start.c
+    tx.c
+)
diff --git a/src/protocol/icmp/alloc.c b/src/protocol/icmp/alloc.c
new file mode 100644
index 0000000..23d7329
--- /dev/null
+++ b/src/protocol/icmp/alloc.c
@@ -0,0 +1,29 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/log.h>
+#include <wip/prv/icmp.h>
+#include <wip/prv/icmp/routines.h>
+#include <wip/prv/icmp/types.h>
+#include <stddef.h>
+
+void *wip_icmp_alloc(struct wip *const w)
+{
+    const struct wip_cfg *const cfg = &w->cfg;
+    const struct wip_icmp z = {0};
+    struct wip_icmp *const ret = cfg->alloc(sizeof *ret, cfg->user);
+
+    if (!ret)
+        return ret;
+
+    *ret = z;
+    ret->next = wip_icmp_rx_start;
+    return ret;
+}
diff --git a/src/protocol/icmp/free.c b/src/protocol/icmp/free.c
new file mode 100644
index 0000000..452e1d4
--- /dev/null
+++ b/src/protocol/icmp/free.c
@@ -0,0 +1,25 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/log.h>
+#include <wip/prv/icmp.h>
+#include <wip/prv/icmp/types.h>
+#include <stddef.h>
+
+void wip_icmp_free(struct wip *const w, void *const args)
+{
+    const struct wip_cfg *const cfg = &w->cfg;
+    struct wip_icmp *const icmp = args;
+
+    if (icmp)
+        cfg->free(icmp->buf, cfg->user);
+
+    cfg->free(icmp, cfg->user);
+}
diff --git a/src/protocol/icmp/rx.c b/src/protocol/icmp/rx.c
new file mode 100644
index 0000000..8e543f9
--- /dev/null
+++ b/src/protocol/icmp/rx.c
@@ -0,0 +1,200 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/io.h>
+#include <wip/prv/log.h>
+#include <wip/prv/icmp.h>
+#include <wip/prv/icmp/types.h>
+#include <stddef.h>
+#include <string.h>
+
+enum
+{
+    TYPE,
+    CHECKSUM = 2,
+    ID = 4,
+    SEQ_NUM = 6,
+    DATA = 8
+};
+
+#if 0
+
+static int get_type(struct wip_icmp *const icmp,
+    const unsigned char *const p, const size_t n)
+{
+    unsigned char type;
+
+    if (icmp->read)
+        return 0;
+
+    type = p[0];
+
+    if (type != ECHO_REQUEST)
+        return -1;
+
+    wip_log("%s: got echo request\n");
+    icmp->type = type;
+    return 0;
+}
+
+static void get_checksum(struct wip_icmp *const icmp,
+    const unsigned char *const p, const size_t n)
+{
+    size_t off;
+    struct wip_be16 v;
+    enum {END = CHECKSUM + sizeof v};
+
+    if (icmp->read >= END || n < END - icmp->read)
+        return;
+
+    off = CHECKSUM - icmp->read;
+    v.v[0] = p[off];
+    v.v[1] = p[off + 1];
+    icmp->exp_checksum = wip_be16(&v);
+}
+
+static void get_id(struct wip_icmp *const icmp, const unsigned char *const p,
+    const size_t n)
+{
+    size_t off;
+    struct wip_be16 v;
+    enum {END = ID + sizeof v};
+
+    if (icmp->read >= END || n < END - icmp->read)
+        return;
+
+    off = ID - icmp->read;
+    v.v[0] = p[off];
+    v.v[1] = p[off + 1];
+    icmp->id = wip_be16(&v);
+}
+
+static void get_seqnum(struct wip_icmp *const icmp, const unsigned char *const p,
+    const size_t n)
+{
+    size_t off;
+    struct wip_be16 v;
+    enum {END = SEQ_NUM + sizeof v};
+
+    if (icmp->read >= END || n < END - icmp->read)
+        return;
+
+    off = SEQ_NUM - icmp->read;
+    v.v[0] = p[off];
+    v.v[1] = p[off + 1];
+    icmp->seqnum = wip_be16(&v);
+    wip_log("chksum=%#x, id=%#x, seq_num=%#x\n", icmp->exp_checksum,
+        icmp->id, icmp->seqnum);
+}
+
+static enum wip_state get_data(struct wip *const w,
+    struct wip_icmp *const icmp, const unsigned char *const p, const size_t n)
+{
+    const struct wip_cfg *const cfg = &w->cfg;
+    const size_t offset = icmp->read + n;
+    const void *src = p;
+    size_t sz = n;
+
+    if (offset < DATA)
+        return WIP_OK;
+    else if (!icmp->buf)
+    {
+        sz = n - DATA - icmp->read;
+        src = p + DATA - icmp->read;
+
+        if (!(icmp->buf = cfg->alloc(sz, cfg->user)))
+            return WIP_FATAL;
+    }
+    else
+    {
+        const size_t nsz = icmp->n + n;
+        enum {MAXSZ = 40};
+        void *buf;
+
+        if (nsz > MAXSZ)
+            return WIP_INVALID;
+        else if (!(buf = cfg->realloc(icmp->buf, nsz, cfg->user)))
+            return WIP_FATAL;
+
+        icmp->buf = buf;
+    }
+
+    memcpy((char *)icmp->buf + icmp->read, src, sz);
+    icmp->n += sz;
+
+    wip_log("data (%lu bytes): {", (unsigned long)icmp->n);
+
+    {
+        size_t i;
+
+        for (i = 0; i < icmp->n; i++)
+        {
+            wip_log("%#hhx", *((const char *)icmp->buf + i));
+
+            if (i + 1 < icmp->n)
+                wip_log(", ");
+        }
+    }
+
+    wip_log("}\n");
+    return WIP_OK;
+}
+#endif
+
+enum wip_state wip_icmp_rx(struct wip *const w, const void *buf,
+    size_t n, void *const args)
+{
+    struct wip_icmp *const icmp = args;
+    enum wip_state ret;
+    size_t r;
+
+    while ((ret = icmp->next(w, buf, n, icmp, &r)) == WIP_AGAIN)
+    {
+        buf = (const char *)buf + r;
+        n -= r;
+    }
+
+    return ret;
+
+#if 0
+    enum wip_state (*next)(struct wip *, const void *, size_t,
+        struct wip_icmp *)
+
+    const struct wip_rx_sm_h *const h = &w->rx.sm.h;
+    const unsigned char *const p = buf;
+    const unsigned short dlen = wip_be16(&h->len) - h->header_sz;
+
+    enum wip_state ret;
+    size_t i;
+
+    if (get_type(icmp, buf, n))
+        return 0;
+
+    get_checksum(icmp, buf, n);
+    get_id(icmp, buf, n);
+    get_seqnum(icmp, buf, n);
+
+    if ((ret = get_data(w, icmp, buf, n)))
+        return ret;
+
+    for (i = 0; i < n; i++)
+        /* Avoid suming checksum */
+        if (icmp->read >= CHECKSUM || ((i != 2) && (i != 3)))
+            icmp->checksum += p[i];
+
+    if (icmp->read += n >= dlen)
+    {
+        wip_log("expected checksum=%#x, got=%#x\n",
+            icmp->exp_checksum, icmp->checksum);
+    }
+
+    return WIP_OK;
+#endif
+}
diff --git a/src/protocol/icmp/start.c b/src/protocol/icmp/start.c
new file mode 100644
index 0000000..f50052e
--- /dev/null
+++ b/src/protocol/icmp/start.c
@@ -0,0 +1,205 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/io.h>
+#include <wip/prv/log.h>
+#include <wip/prv/icmp.h>
+#include <wip/prv/icmp/routines.h>
+#include <wip/prv/icmp/types.h>
+#include <stddef.h>
+#include <string.h>
+
+struct read
+{
+    const void *buf;
+    size_t n;
+    struct wip_icmp *icmp;
+};
+
+static int io_read(void *const buf, const size_t n, void *const user)
+{
+    const struct read *const r = user;
+    const size_t ret = n > r->n ? r->n : n;
+
+    memcpy(buf, r->buf, ret);
+    return ret;
+}
+
+static enum wip_state readbuf(struct wip_sm_io *const io, const void *const buf,
+    const size_t n, struct wip_icmp *const icmp)
+{
+    struct wip_cfg cfg = {0};
+    struct read r;
+
+    r.buf = buf;
+    r.n = n;
+    r.icmp = icmp;
+
+    cfg.read = io_read;
+    cfg.user = &r;
+    return wip_io_read_c(&cfg, io);
+}
+
+enum wip_state get_payload(struct wip *const w, const void *const buf,
+    const size_t n, struct wip_icmp *const icmp, size_t *const r)
+{
+    const struct wip_cfg *const cfg = &w->cfg;
+    const size_t nsz = icmp->read + n;
+    char *const nbuf = cfg->realloc(icmp->buf, nsz, cfg->user);
+    size_t i;
+
+    if (!nbuf)
+        return WIP_FATAL;
+
+    memcpy(nbuf + icmp->read, buf, n);
+    icmp->buf = nbuf;
+    icmp->read += n;
+    *r = n;
+
+    for (i = icmp->read; i < nsz; i++)
+        icmp->checksum += *(const char *)icmp->buf;
+
+    wip_log("ICMP data={");
+
+    for (i = 0; i < icmp->read; i++)
+    {
+        wip_log("%#hhx", *((const char *)icmp->buf + i));
+
+        if (i + 1 < icmp->read)
+            wip_log(", ");
+    }
+
+    wip_log("}\n");
+
+    wip_log("calculated checksum: %#hx, expected checksum: %#hx\n",
+        icmp->checksum, wip_be16(&icmp->exp_checksum));
+    return WIP_OK;
+}
+
+enum wip_state get_seqnum(struct wip *const w, const void *const buf,
+    const size_t n, struct wip_icmp *const icmp, size_t *const r)
+{
+    const enum wip_state state = readbuf(&icmp->io, buf, n, icmp);
+
+    if (state)
+        return state;
+    else
+    {
+        struct wip_sm_io io = {0};
+
+        io.buf = &icmp->seqnum;
+        io.n = sizeof icmp->seqnum;
+        icmp->io = io;
+    }
+
+    wip_log("got seqnum: %#x\n", wip_be16(&icmp->seqnum));
+    icmp->checksum += wip_be16(&icmp->seqnum);
+    icmp->next = get_payload;
+    *r = sizeof icmp->seqnum;
+    return WIP_AGAIN;
+}
+
+enum wip_state get_id(struct wip *const w, const void *const buf,
+    const size_t n, struct wip_icmp *const icmp, size_t *const r)
+{
+    const enum wip_state state = readbuf(&icmp->io, buf, n, icmp);
+
+    if (state)
+        return state;
+    else
+    {
+        struct wip_sm_io io = {0};
+
+        io.buf = &icmp->seqnum;
+        io.n = sizeof icmp->seqnum;
+        icmp->io = io;
+    }
+
+    wip_log("got id: %#x\n", wip_be16(&icmp->id));
+    icmp->checksum += wip_be16(&icmp->id);
+    icmp->next = get_seqnum;
+    *r = sizeof icmp->id;
+    return WIP_AGAIN;
+}
+
+enum wip_state get_checksum(struct wip *const w, const void *const buf,
+    const size_t n, struct wip_icmp *const icmp, size_t *const r)
+{
+    const enum wip_state state = readbuf(&icmp->io, buf, n, icmp);
+
+    if (state)
+        return state;
+    else
+    {
+        struct wip_sm_io io = {0};
+
+        io.buf = &icmp->id;
+        io.n = sizeof icmp->id;
+        icmp->io = io;
+    }
+
+    wip_log("got expected checksum: %#x\n", wip_be16(&icmp->exp_checksum));
+    icmp->next = get_id;
+    *r = sizeof icmp->exp_checksum;
+    return WIP_AGAIN;
+}
+
+enum wip_state get_code(struct wip *const w, const void *const buf,
+    const size_t n, struct wip_icmp *const icmp, size_t *const r)
+{
+    unsigned char code;
+    struct wip_sm_io io = {0};
+    enum wip_state state;
+
+    io.buf = &code;
+    io.n = sizeof code;
+
+    if ((state = readbuf(&io, buf, n, icmp)))
+        return state;
+    else if (code)
+        return WIP_INVALID;
+    else
+    {
+        struct wip_sm_io nio = {0};
+
+        nio.buf = &icmp->exp_checksum;
+        nio.n = sizeof icmp->exp_checksum;
+        icmp->io = nio;
+    }
+
+    wip_log("got code\n");
+    icmp->checksum += code;
+    icmp->next = get_checksum;
+    *r = sizeof code;
+    return WIP_AGAIN;
+}
+
+enum wip_state wip_icmp_rx_start(struct wip *const w, const void *const buf,
+    const size_t n, struct wip_icmp *const icmp, size_t *const r)
+{
+    unsigned char type;
+    struct wip_sm_io io = {0};
+    enum wip_state state;
+
+    io.buf = &type;
+    io.n = sizeof type;
+
+    if ((state = readbuf(&io, buf, n, icmp)))
+        return state;
+    else if (type != ICMP_ECHO_REQUEST)
+        return WIP_INVALID;
+
+    wip_log("got echo request\n");
+    icmp->checksum += type;
+    icmp->type = type;
+    icmp->next = get_code;
+    *r = sizeof type;
+    return WIP_AGAIN;
+}
diff --git a/src/protocol/icmp/tx.c b/src/protocol/icmp/tx.c
new file mode 100644
index 0000000..27fe876
--- /dev/null
+++ b/src/protocol/icmp/tx.c
@@ -0,0 +1,21 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/log.h>
+#include <wip/prv/icmp.h>
+#include <wip/prv/icmp/types.h>
+#include <stddef.h>
+
+int wip_icmp_tx(struct wip *const wip, void *const buf, const size_t n,
+    void *const args)
+{
+    wip_log("%s: TODO\n");
+    return 0;
+}
diff --git a/src/protocol/tcp/CMakeLists.txt b/src/protocol/tcp/CMakeLists.txt
new file mode 100644
index 0000000..0caec18
--- /dev/null
+++ b/src/protocol/tcp/CMakeLists.txt
@@ -0,0 +1,13 @@
+# wip, a small TCP/IP stack.
+# Copyright (C) 2025  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+target_sources(${PROJECT_NAME} PRIVATE
+    alloc.c
+    free.c
+    rx.c
+    tx.c
+)
diff --git a/src/protocol/tcp/alloc.c b/src/protocol/tcp/alloc.c
new file mode 100644
index 0000000..c90f1c9
--- /dev/null
+++ b/src/protocol/tcp/alloc.c
@@ -0,0 +1,20 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/log.h>
+#include <wip/prv/tcp.h>
+#include <wip/prv/tcp/types.h>
+#include <stddef.h>
+
+void *wip_tcp_alloc(struct wip *const w)
+{
+    wip_log("%s: TODO\n", __func__);
+    return NULL;
+}
diff --git a/src/protocol/tcp/free.c b/src/protocol/tcp/free.c
new file mode 100644
index 0000000..ddde038
--- /dev/null
+++ b/src/protocol/tcp/free.c
@@ -0,0 +1,19 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/log.h>
+#include <wip/prv/tcp.h>
+#include <wip/prv/tcp/types.h>
+#include <stddef.h>
+
+void wip_tcp_free(struct wip *const w, void *const args)
+{
+    wip_log("%s: TODO\n", __func__);
+}
diff --git a/src/protocol/tcp/rx.c b/src/protocol/tcp/rx.c
new file mode 100644
index 0000000..6b23546
--- /dev/null
+++ b/src/protocol/tcp/rx.c
@@ -0,0 +1,21 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/log.h>
+#include <wip/prv/tcp.h>
+#include <wip/prv/tcp/types.h>
+#include <stddef.h>
+
+enum wip_state wip_tcp_rx(struct wip *const wip, const void *const buf,
+    const size_t n, void *const args)
+{
+    wip_log("%s: TODO\n");
+    return WIP_OK;
+}
diff --git a/src/protocol/tcp/tx.c b/src/protocol/tcp/tx.c
new file mode 100644
index 0000000..55524e3
--- /dev/null
+++ b/src/protocol/tcp/tx.c
@@ -0,0 +1,21 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/log.h>
+#include <wip/prv/tcp.h>
+#include <wip/prv/tcp/types.h>
+#include <stddef.h>
+
+int wip_tcp_tx(struct wip *const wip, void *const buf, const size_t n,
+    void *const args)
+{
+    wip_log("%s: TODO\n");
+    return 0;
+}
diff --git a/src/protocol/udp/CMakeLists.txt b/src/protocol/udp/CMakeLists.txt
new file mode 100644
index 0000000..0caec18
--- /dev/null
+++ b/src/protocol/udp/CMakeLists.txt
@@ -0,0 +1,13 @@
+# wip, a small TCP/IP stack.
+# Copyright (C) 2025  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+target_sources(${PROJECT_NAME} PRIVATE
+    alloc.c
+    free.c
+    rx.c
+    tx.c
+)
diff --git a/src/protocol/udp/alloc.c b/src/protocol/udp/alloc.c
new file mode 100644
index 0000000..d812ea5
--- /dev/null
+++ b/src/protocol/udp/alloc.c
@@ -0,0 +1,20 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/log.h>
+#include <wip/prv/udp.h>
+#include <wip/prv/udp/types.h>
+#include <stddef.h>
+
+void *wip_udp_alloc(struct wip *const w)
+{
+    wip_log("%s: TODO\n", __func__);
+    return NULL;
+}
diff --git a/src/protocol/udp/free.c b/src/protocol/udp/free.c
new file mode 100644
index 0000000..c6354fb
--- /dev/null
+++ b/src/protocol/udp/free.c
@@ -0,0 +1,19 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/log.h>
+#include <wip/prv/udp.h>
+#include <wip/prv/udp/types.h>
+#include <stddef.h>
+
+void wip_udp_free(struct wip *const w, void *const args)
+{
+    wip_log("%s: TODO\n", __func__);
+}
diff --git a/src/protocol/udp/rx.c b/src/protocol/udp/rx.c
new file mode 100644
index 0000000..29aa4cc
--- /dev/null
+++ b/src/protocol/udp/rx.c
@@ -0,0 +1,21 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/log.h>
+#include <wip/prv/udp.h>
+#include <wip/prv/udp/types.h>
+#include <stddef.h>
+
+enum wip_state wip_udp_rx(struct wip *const wip, const void *const buf,
+    const size_t n, void *const args)
+{
+    wip_log("%s: TODO\n");
+    return WIP_OK;
+}
diff --git a/src/protocol/udp/tx.c b/src/protocol/udp/tx.c
new file mode 100644
index 0000000..a29ec0f
--- /dev/null
+++ b/src/protocol/udp/tx.c
@@ -0,0 +1,21 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/log.h>
+#include <wip/prv/udp.h>
+#include <wip/prv/udp/types.h>
+#include <stddef.h>
+
+int wip_udp_tx(struct wip *const wip, void *const buf, const size_t n,
+    void *const args)
+{
+    wip_log("%s: TODO\n");
+    return 0;
+}
diff --git a/src/routines/CMakeLists.txt b/src/routines/CMakeLists.txt
new file mode 100644
index 0000000..aa69a13
--- /dev/null
+++ b/src/routines/CMakeLists.txt
@@ -0,0 +1,10 @@
+# wip, a small TCP/IP stack.
+# Copyright (C) 2025  Xavier Del Campo Romero
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+target_sources(${PROJECT_NAME} PRIVATE
+    rx.c
+)
diff --git a/src/routines/rx.c b/src/routines/rx.c
new file mode 100644
index 0000000..b031d14
--- /dev/null
+++ b/src/routines/rx.c
@@ -0,0 +1,447 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/io.h>
+#include <wip/prv/log.h>
+#include <wip/prv/icmp.h>
+#include <wip/prv/tcp.h>
+#include <wip/prv/udp.h>
+#include <wip/prv/routines.h>
+#include <stddef.h>
+
+#include <time.h>
+
+unsigned valid_packets;
+
+enum {MIN_HEADER_SZ = 20};
+
+static const struct wip_prot_ops protocols[] =
+{
+    {
+        WIP_P_ICMP,
+        wip_icmp_alloc,
+        wip_icmp_free,
+        wip_icmp_rx,
+        wip_icmp_tx
+    },
+
+    {
+        WIP_P_TCP,
+        wip_tcp_alloc,
+        wip_tcp_free,
+        wip_tcp_rx,
+        wip_tcp_tx
+    },
+
+    {
+        WIP_P_UDP,
+        wip_udp_alloc,
+        wip_udp_free,
+        wip_udp_rx,
+        wip_udp_tx
+    }
+};
+
+static enum wip_state get_data(struct wip *const w)
+{
+    struct wip_rx *const rx = &w->rx;
+    struct wip_rx_sm_h *const h = &rx->sm.h;
+    struct wip_sm_io *const io = &h->io;
+    const unsigned short dlen = wip_be16(&h->len) - h->header_sz;
+    const struct wip_prot_ops *const p = h->prot;
+    enum wip_state n;
+
+    if ((n = wip_io_read(w, io)))
+        return n;
+    else if (p && (n = p->rx(w, rx->buf, io->n, h->args)))
+        return n;
+
+#if 0
+    wip_log("got new data, h->i=%lu, io->n=%lu, dlen=%u\n",
+        (unsigned long)h->i, (unsigned long)io->n, dlen);
+#endif
+
+    if ((h->i += io->n) >= dlen)
+    {
+#if 1
+        wip_log("finished getting data (%u bytes)\n", (unsigned)dlen);
+#endif
+        if (h->prot)
+        {
+            h->prot->free(w, h->args);
+            h->prot = h->args = NULL;
+        }
+
+        wip_rx(w);
+        valid_packets++;
+    }
+    else
+    {
+        struct wip_sm_io nio = {0};
+        const size_t n = dlen - h->i;
+
+#if 0
+        wip_log("still need more data! (%u bytes)\n", n);
+#endif
+
+        nio.buf = rx->buf;
+        nio.n = n > sizeof rx->buf ? sizeof rx->buf : n;
+        *io = nio;
+    }
+
+    return WIP_OK;
+}
+
+static enum wip_state get_options(struct wip *const w)
+{
+    unsigned char b;
+    struct wip_rx *const rx = &w->rx;
+    struct wip_rx_sm_h *const h = &rx->sm.h;
+    struct wip_sm_io io = {0};
+    enum wip_state n;
+
+    io.buf = &b;
+    io.n = sizeof b;
+
+    if ((n = wip_io_read(w, &io)))
+        return n;
+    else if (++h->i >= h->header_sz - MIN_HEADER_SZ)
+    {
+        struct wip_sm_io nio = {0};
+        const unsigned short dlen = wip_be16(&h->len);
+        const size_t n = dlen - h->i;
+
+        nio.buf = rx->buf;
+        nio.n = n > sizeof rx->buf ? sizeof rx->buf : n;
+        h->io = nio;
+        h->i = 0;
+#if 0
+        wip_log("%s: will read %lu bytes of data\n", __func__, (unsigned long)h->io.n);
+#endif
+        rx->next = get_data;
+    }
+
+    h->chksum += b;
+    return WIP_OK;
+}
+
+static enum wip_state get_dst(struct wip *const w)
+{
+    struct wip_rx *const rx = &w->rx;
+    struct wip_rx_sm_h *const h = &rx->sm.h;
+    const enum wip_state n = wip_io_read(w, &h->io);
+
+    if (n)
+        return n;
+
+#if 0
+    wip_log("got dst address=%hhu.%hhu.%hhu.%hhu\n",
+        h->src.v[0], h->src.v[1], h->src.v[2], h->src.v[3]);
+#endif
+    h->chksum += wip_be32(&h->dst);
+
+    if (h->header_sz > MIN_HEADER_SZ)
+    {
+#if 0
+        wip_log("will parse options\n");
+#endif
+        rx->next = get_options;
+    }
+    else
+    {
+        struct wip_sm_io io = {0};
+        const size_t n = wip_be16(&h->len) - h->header_sz;
+
+        io.buf = rx->buf;
+        io.n = n >= sizeof rx->buf ? sizeof rx->buf : n;
+#if 0
+        wip_log("%s: expecting %lu bytes of data\n", __func__, (unsigned long)io.n);
+#endif
+        h->i = 0;
+        h->io = io;
+        rx->next = get_data;
+    }
+
+    return WIP_OK;
+}
+
+static enum wip_state get_src(struct wip *const w)
+{
+    struct wip_rx *const rx = &w->rx;
+    struct wip_rx_sm_h *const h = &rx->sm.h;
+    const enum wip_state n = wip_io_read(w, &h->io);
+
+    if (n)
+        return n;
+    else
+    {
+        struct wip_sm_io io = {0};
+
+        io.buf = &h->dst;
+        io.n = sizeof h->dst;
+        h->io = io;
+    }
+
+#if 0
+    wip_log("got source address=%hhu.%hhu.%hhu.%hhu\n",
+        h->src.v[0], h->src.v[1], h->src.v[2], h->src.v[3]);
+#endif
+    h->chksum += wip_be32(&h->src);
+    rx->next = get_dst;
+    return WIP_OK;
+}
+
+static enum wip_state get_chksum(struct wip *const w)
+{
+    struct wip_rx *const rx = &w->rx;
+    struct wip_rx_sm_h *const h = &rx->sm.h;
+    const enum wip_state n = wip_io_read(w, &h->io);
+
+    if (n)
+        return n;
+    else
+    {
+        struct wip_sm_io io = {0};
+
+        io.buf = &h->src;
+        io.n = sizeof h->src;
+        h->io = io;
+    }
+
+#if 0
+    wip_log("got expected checksum=%hu\n", wip_be16(&h->rchksum));
+#endif
+    rx->next = get_src;
+    return WIP_OK;
+}
+
+static const struct wip_prot_ops *get_ops(const unsigned char protocol)
+{
+    size_t i;
+
+    for (i = 0; i < sizeof protocols / sizeof *protocols; i++)
+    {
+        const struct wip_prot_ops *const p = &protocols[i];
+
+        if (protocol == p->id)
+            return p;
+    }
+
+    return NULL;
+}
+
+static enum wip_state get_protocol(struct wip *const w)
+{
+    struct wip_rx *const rx = &w->rx;
+    struct wip_rx_sm_h *const h = &rx->sm.h;
+    struct wip_sm_io io = {0};
+    enum wip_state n;
+
+    io.buf = &h->protocol;
+    io.n = sizeof h->protocol;
+
+    if ((n = wip_io_read(w, &io)))
+        return n;
+    else
+    {
+        struct wip_sm_io io = {0};
+
+        io.buf = &h->rchksum;
+        io.n = sizeof h->rchksum;
+        h->io = io;
+    }
+
+#if 0
+    wip_log("got protocol: %#hhx\n", h->protocol);
+#endif
+    if ((h->prot = get_ops(h->protocol))
+        && !(h->args = h->prot->alloc(w)))
+        return WIP_FATAL;
+
+    h->chksum += h->protocol;
+    rx->next = get_chksum;
+    return WIP_OK;
+}
+
+static enum wip_state get_ttl(struct wip *const w)
+{
+    struct wip_rx *const rx = &w->rx;
+    struct wip_rx_sm_h *const h = &rx->sm.h;
+    struct wip_sm_io io = {0};
+    enum wip_state n;
+
+    io.buf = &h->ttl;
+    io.n = sizeof h->ttl;
+
+    if ((n = wip_io_read(w, &io)))
+        return n;
+
+#if 0
+    wip_log("got TTL\n");
+#endif
+    h->chksum += h->ttl;
+    rx->next = get_protocol;
+    return WIP_OK;
+}
+
+static enum wip_state get_flags_offset(struct wip *const w)
+{
+    unsigned char flags;
+    unsigned short fl_off;
+    struct wip_rx *const rx = &w->rx;
+    struct wip_rx_sm_h *const h = &rx->sm.h;
+    const enum wip_state n = wip_io_read(w, &h->io);
+
+    if (n)
+        return n;
+
+    fl_off = wip_be16(&h->fl_off);
+
+    if ((flags = fl_off >> 13) & 1)
+        return WIP_INVALID;
+
+#if 0
+    wip_log("got flags offset: %hu\n", fl_off);
+#endif
+    h->chksum += fl_off;
+    rx->next = get_ttl;
+    return WIP_OK;
+}
+
+static enum wip_state get_id(struct wip *const w)
+{
+    struct wip_rx *const rx = &w->rx;
+    struct wip_rx_sm_h *const h = &rx->sm.h;
+    const enum wip_state n = wip_io_read(w, &h->io);
+
+    /* TODO: use ID? */
+    if (n)
+        return n;
+    else
+    {
+        struct wip_sm_io io = {0};
+
+        io.buf = &h->fl_off;
+        io.n = sizeof h->fl_off;
+        h->io = io;
+    }
+
+#if 0
+    wip_log("got id: %hu\n", wip_be16(&h->id));
+#endif
+    h->chksum += wip_be16(&h->id);
+    rx->next = get_flags_offset;
+    return WIP_OK;
+}
+
+static enum wip_state get_len(struct wip *const w)
+{
+    unsigned short len;
+    struct wip_rx *const rx = &w->rx;
+    struct wip_rx_sm_h *const h = &rx->sm.h;
+    const enum wip_state n = wip_io_read(w, &h->io);
+
+    if (n)
+        return n;
+    else if ((len = wip_be16(&h->len)) < MIN_HEADER_SZ)
+        return WIP_INVALID;
+    else if (len > sizeof rx->buf)
+    {
+#if 0
+        wip_log("data too big: %hu (max %lu)\n", len,
+            (unsigned long)sizeof rx->buf);
+#endif
+        return WIP_INVALID;
+    }
+    else
+    {
+        struct wip_sm_io io = {0};
+
+        io.buf = &h->id;
+        io.n = sizeof h->id;
+        h->io = io;
+    }
+
+#if 0
+    wip_log("got length: %hu\n", len);
+#endif
+    h->chksum = len;
+    rx->next = get_id;
+    return WIP_OK;
+}
+
+static enum wip_state get_dscp_ecn(struct wip *const w)
+{
+    unsigned char b;
+    struct wip_rx *const rx = &w->rx;
+    struct wip_rx_sm_h *const h = &rx->sm.h;
+    struct wip_sm_io io = {0};
+    enum wip_state n;
+
+    io.buf = &b;
+    io.n = sizeof b;
+
+    /* TODO: support DSCP and ECN? */
+    if ((n = wip_io_read(w, &io)))
+        return n;
+    else
+    {
+        struct wip_rx_sm_h *const h = &rx->sm.h;
+        struct wip_sm_io io = {0};
+
+        io.buf = &h->len;
+        io.n = sizeof h->len;
+        h->io = io;
+    }
+
+#if 0
+    wip_log("got DSCP and ECN\n");
+#endif
+    h->chksum += b;
+    rx->next = get_len;
+    return WIP_OK;
+}
+
+static enum wip_state get_version_ihl(struct wip *const w)
+{
+    enum {VERSION = 4};
+    unsigned char b, version, ihl;
+    struct wip_rx *const rx = &w->rx;
+    struct wip_rx_sm_h *const h = &rx->sm.h;
+    struct wip_sm_io io = {0};
+    enum wip_state n;
+
+    io.buf = &b;
+    io.n = sizeof b;
+
+    if ((n = wip_io_read(w, &io)))
+        return n;
+    else if ((version = b >> 4) != 4
+        || (ihl = b & 0xf) < MIN_HEADER_SZ / 4)
+        return WIP_INVALID;
+
+#if 0
+    wip_log("got IPv4 header, length=%u\n", ihl * 4);
+#endif
+    h->chksum += b;
+    h->header_sz = ihl * 4;
+    rx->next = get_dscp_ecn;
+    return WIP_OK;
+}
+
+void wip_rx(struct wip *const w)
+{
+    const struct wip_rx_sm_h h = {0};
+    struct wip_rx *const rx = &w->rx;
+    struct wip_rx_sm_h *const ph = &rx->sm.h;
+
+    *ph = h;
+    rx->next = get_version_ihl;
+}
diff --git a/src/run.c b/src/run.c
new file mode 100644
index 0000000..8ef952f
--- /dev/null
+++ b/src/run.c
@@ -0,0 +1,49 @@
+/*
+ * wip, a small TCP/IP stack.
+ * Copyright (C) 2025  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <wip/wip.h>
+#include <wip/prv/routines.h>
+
+int wip_run(struct wip *const w)
+{
+    enum wip_state n;
+
+again:
+
+    switch ((n = w->rx.next(w)))
+    {
+        case WIP_OK:
+            goto again;
+
+        case WIP_AGAIN:
+            break;
+
+        case WIP_FATAL:
+            return -1;
+
+        case WIP_INVALID:
+            wip_rx(w);
+            break;
+    }
+
+#if 0
+    switch (w->tx.next(w))
+    {
+        case WIP_OK:
+        case WIP_AGAIN:
+            break;
+
+        case WIP_INVALID:
+        case WIP_FATAL:
+            return -1;
+    }
+#endif
+
+    return 0;
+}