Send HTTP headers to payload callback

Even if libweb already parses some common headers, such as
Content-Length, some users might find it interesting to inspect which
headers were received from a request.

Since HTTP/1.1 does not define a limit on the number of maximum headers
a client can send, for security reasons a maximum value must be provided
by the user. Any extra headers shall be then discarded by libweb.

An example application showing this new feature is also provided.

12 files changed, 232 insertions, 13 deletions

diff --git a/doc/man7/libweb_handler.7 b/doc/man7/libweb_handler.7
index 5c910e0..b9fd53f 100644
--- a/doc/man7/libweb_handler.7
+++ b/doc/man7/libweb_handler.7
@@ -1,4 +1,4 @@
-.TH LIBWEB_HANDLER 7 2023-09-15 0.1.0 "libweb Library Reference"
+.TH LIBWEB_HANDLER 7 2023-11-18 0.2.0 "libweb Library Reference"
 
 .SH NAME
 libweb_handler \- libweb high-level website configuration
@@ -69,15 +69,17 @@ struct handler_cfg
     const char *\fItmpdir\fP;
     int (*\fIlength\fP)(unsigned long long len, const struct http_cookie *c, struct http_response *r, void *user);
     void *\fIuser\fP;
+    size_t \fImax_headers\fP;
 };
 .EE
 .in
 .PP
 
 .IR tmpdir ,
-.I length
-and
+.IR length ,
 .I user
+and
+.I max_headers
 are passed directly to the
 .I struct http_cfg
 object used to initialize a
diff --git a/doc/man7/libweb_http.7 b/doc/man7/libweb_http.7
index 329a616..93bb882 100644
--- a/doc/man7/libweb_http.7
+++ b/doc/man7/libweb_http.7
@@ -1,4 +1,4 @@
-.TH LIBWEB_HTTP 7 2023-09-15 0.1.0 "libweb Library Reference"
+.TH LIBWEB_HTTP 7 2023-11-18 0.2.0 "libweb Library Reference"
 
 .SH NAME
 libweb_http \- libweb HTTP connection handling and utilities
@@ -84,6 +84,7 @@ struct http_cfg
     int (*\fIlength\fP)(unsigned long long \fIlen\fP, const struct http_cookie *\fIc\fP, struct http_response *\fIr\fP, void *\fIuser\fP);
     const char *\fItmpdir\fP;
     void *\fIuser\fP;
+    size_t \fImax_headers\fP;
 };
 .EE
 .in
@@ -195,6 +196,15 @@ other function pointers defined by
 .I user
 can be a null pointer.
 
+.I max_headers
+refers to the maximum number of header fields that shall be passed to the
+.IR "struct http_payload"
+object passed to the function pointed to by
+.IR payload .
+Any extra headers sent by the client outside this maximum value shall be
+silently ignored by
+.IR libweb .
+
 .SS HTTP payload
 
 When a client submits a request to the server,
@@ -224,6 +234,8 @@ struct http_payload
 
     const struct http_arg *\fIargs\fP;
     size_t \fIn_args\fP;
+    const struct http_header *\fIheaders\fP;
+    size_t \fIn_headers\fP;
 };
 .EE
 .in
@@ -260,6 +272,11 @@ defines a list of key-value pairs containing URL parameters. Its length
 is defined by
 .IR n_args .
 
+.I headers
+defines a list of key-value pairs containing header fields. Its length
+is defined by
+.IR n_headers .
+
 .SS HTTP POST payload
 
 As opposed to payload-less HTTP/1.1 operations, such as
diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index d9bf4cc..7353458 100644
--- a/examples/CMakeLists.txt
+++ b/examples/CMakeLists.txt
@@ -1,3 +1,4 @@
 cmake_minimum_required(VERSION 3.13)
+add_subdirectory(headers)
 add_subdirectory(hello)
 add_subdirectory(html)
diff --git a/examples/Makefile b/examples/Makefile
index b26a13a..672f209 100644
--- a/examples/Makefile
+++ b/examples/Makefile
@@ -1,6 +1,7 @@
 .POSIX:
 
 all: \
+	headers \
 	hello \
 	html
 
@@ -10,6 +11,9 @@ clean:
 
 FORCE:
 
+headers: FORCE
+	+cd headers && $(MAKE)
+
 hello: FORCE
 	+cd hello && $(MAKE)
 
diff --git a/examples/headers/CMakeLists.txt b/examples/headers/CMakeLists.txt
new file mode 100644
index 0000000..8c91fd7
--- /dev/null
+++ b/examples/headers/CMakeLists.txt
@@ -0,0 +1,4 @@
+cmake_minimum_required(VERSION 3.13)
+project(headers C)
+add_executable(${PROJECT_NAME} main.c)
+target_link_libraries(${PROJECT_NAME} PRIVATE web)
diff --git a/examples/headers/Makefile b/examples/headers/Makefile
new file mode 100644
index 0000000..4905fbd
--- /dev/null
+++ b/examples/headers/Makefile
@@ -0,0 +1,26 @@
+.POSIX:
+
+PROJECT = headers
+DEPS = \
+	main.o
+LIBWEB = ../../libweb.a
+DYNSTR = ../../dynstr/libdynstr.a
+CFLAGS = -I ../../include -I ../../dynstr/include
+LIBWEB_FLAGS = -L ../../ -l web
+DYNSTR_FLAGS = -L ../../dynstr -l dynstr
+
+all: $(PROJECT)
+
+clean:
+	rm -f $(DEPS)
+
+FORCE:
+
+$(PROJECT): $(DEPS) $(LIBWEB) $(DYNSTR)
+	$(CC) $(LDFLAGS) $(DEPS) $(LIBWEB_FLAGS) $(DYNSTR_FLAGS) -o $@
+
+$(LIBWEB): FORCE
+	+cd ../../ && $(MAKE)
+
+$(DYNSTR): FORCE
+	+cd ../../dynstr && $(MAKE)
diff --git a/examples/headers/README.md b/examples/headers/README.md
new file mode 100644
index 0000000..01c243a
--- /dev/null
+++ b/examples/headers/README.md
@@ -0,0 +1,16 @@
+# HTTP headers example
+
+This example shows a HTTP/1.1 server that listens to port `8080` and prints
+the headers received from the client (up to a maximum of `max_headers`) to
+standard output.
+
+## How to build
+
+If using `make(1)`, just run `make` from this directory.
+
+If using CMake, examples are built by default when configuring the project
+from [the top-level `CMakeLists.txt`](../../CMakeLists.txt).
+
+## How to run
+
+Run the executable without any command line arguments.
diff --git a/examples/headers/main.c b/examples/headers/main.c
new file mode 100644
index 0000000..b465aa1
--- /dev/null
+++ b/examples/headers/main.c
@@ -0,0 +1,81 @@
+#include <dynstr.h>
+#include <libweb/handler.h>
+#include <libweb/html.h>
+#include <libweb/http.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static const size_t max_headers = 5;
+
+static int hello(const struct http_payload *const pl,
+    struct http_response *const r, void *const user)
+{
+    printf("Got %zu headers from the client (max %zu).\n",
+        pl->n_headers, max_headers);
+
+    for (size_t i = 0; i < pl->n_headers; i++)
+    {
+        const struct http_header *const h = &pl->headers[i];
+
+        printf("%s: %s\n", h->header, h->value);
+    }
+
+    *r = (const struct http_response)
+    {
+        .status = HTTP_STATUS_OK
+    };
+
+    return 0;
+}
+
+static int on_length(const unsigned long long len,
+    const struct http_cookie *const c, struct http_response *const r,
+    void *const user)
+{
+    *r = (const struct http_response)
+    {
+        .status = HTTP_STATUS_FORBIDDEN
+    };
+
+    return 1;
+}
+
+int main(int argc, char *argv[])
+{
+    int ret = EXIT_FAILURE;
+    const short port = 8080;
+    const struct handler_cfg cfg =
+    {
+        .length = on_length,
+        .max_headers = max_headers
+    };
+
+    struct handler *const h = handler_alloc(&cfg);
+    static const char *const urls[] = {"/", "/index.html"};
+
+    if (!h)
+    {
+        fprintf(stderr, "%s: handler_alloc failed\n", __func__);
+        goto end;
+    }
+
+    for (size_t i = 0; i < sizeof urls / sizeof *urls; i++)
+        if (handler_add(h, urls[i], HTTP_OP_GET, hello, NULL))
+        {
+            fprintf(stderr, "%s: handler_add failed\n", __func__);
+            goto end;
+        }
+
+    if (handler_listen(h, port))
+    {
+        fprintf(stderr, "%s: handler_listen failed\n", __func__);
+        goto end;
+    }
+
+    ret = EXIT_SUCCESS;
+
+end:
+    handler_free(h);
+    return ret;
+}
diff --git a/handler.c b/handler.c
index 61a2806..f6e47a3 100644
--- a/handler.c
+++ b/handler.c
@@ -109,7 +109,8 @@ static struct client *find_or_alloc_client(struct handler *const h,
         .payload = on_payload,
         .length = on_length,
         .user = ret,
-        .tmpdir = h->cfg.tmpdir
+        .tmpdir = h->cfg.tmpdir,
+        .max_headers = h->cfg.max_headers
     };
 
     *ret = (const struct client)
diff --git a/http.c b/http.c
index 48a5ab0..80086e1 100644
--- a/http.c
+++ b/http.c
@@ -88,7 +88,8 @@ struct http_ctx
         } u;
 
         struct http_arg *args;
-        size_t n_args;
+        size_t n_args, n_headers;
+        struct http_header *headers;
     } ctx;
 
     struct write_ctx
@@ -475,6 +476,15 @@ static void ctx_free(struct ctx *const c)
     for (size_t i = 0; i < c->n_args; i++)
         arg_free(&c->args[i]);
 
+    for (size_t i = 0; i < c->n_headers; i++)
+    {
+        const struct http_header *const hdr = &c->headers[i];
+
+        free(hdr->header);
+        free(hdr->value);
+    }
+
+    free(c->headers);
     free(c->args);
     *c = (const struct ctx){0};
 }
@@ -946,7 +956,9 @@ static struct http_payload ctx_to_payload(const struct ctx *const c)
         .op = c->op,
         .resource = c->resource,
         .args = c->args,
-        .n_args = c->n_args
+        .n_args = c->n_args,
+        .headers = c->headers,
+        .n_headers = c->n_headers
     };
 }
 
@@ -1020,6 +1032,56 @@ static int expect(struct http_ctx *const h, const char *const value)
     return 0;
 }
 
+static int append_header(struct http_ctx *const h, const char *const line,
+    const size_t n, const char *const value)
+{
+    struct ctx *const c = &h->ctx;
+
+    if (c->n_headers >= h->cfg.max_headers)
+        return 0;
+
+    struct http_header *const headers = realloc(c->headers,
+        (c->n_headers + 1) * sizeof *headers);
+    char *headerdup = NULL, *valuedup = NULL;
+    int ret = -1;
+
+    if (!headers)
+    {
+        fprintf(stderr, "%s: realloc(3): %s\n", __func__, strerror(errno));
+        return -1;
+    }
+
+    c->headers = headers;
+
+    if (!(headerdup = strndup(line, n)))
+    {
+        fprintf(stderr, "%s: strndup(3): %s\n", __func__, strerror(errno));
+        goto end;
+    }
+    else if (!(valuedup = strdup(value)))
+    {
+        fprintf(stderr, "%s: strdup(3): %s\n", __func__, strerror(errno));
+        goto end;
+    }
+
+    c->headers[c->n_headers++] = (const struct http_header)
+    {
+        .header = headerdup,
+        .value = valuedup
+    };
+
+    ret = 0;
+
+end:
+    if (ret)
+    {
+        free(headerdup);
+        free(valuedup);
+    }
+
+    return ret;
+}
+
 static int process_header(struct http_ctx *const h, const char *const line,
     const size_t n, const char *const value)
 {
@@ -1059,7 +1121,7 @@ static int process_header(struct http_ctx *const h, const char *const line,
             return ret;
     }
 
-    return 0;
+    return append_header(h, line, n, value);
 }
 
 static int check_length(struct http_ctx *const h)
diff --git a/include/libweb/handler.h b/include/libweb/handler.h
index 9cde129..f7bc76a 100644
--- a/include/libweb/handler.h
+++ b/include/libweb/handler.h
@@ -13,6 +13,7 @@ struct handler_cfg
     int (*length)(unsigned long long len, const struct http_cookie *c,
         struct http_response *r, void *user);
     void *user;
+    size_t max_headers;
 };
 
 struct handler *handler_alloc(const struct handler_cfg *cfg);
diff --git a/include/libweb/http.h b/include/libweb/http.h
index 80030fb..ddb6a89 100644
--- a/include/libweb/http.h
+++ b/include/libweb/http.h
@@ -5,6 +5,11 @@
 #include <stddef.h>
 #include <stdio.h>
 
+struct http_header
+{
+    char *header, *value;
+};
+
 struct http_payload
 {
     enum http_op
@@ -46,7 +51,8 @@ struct http_payload
         char *key, *value;
     } *args;
 
-    size_t n_args;
+    size_t n_args, n_headers;
+    const struct http_header *headers;
 };
 
 #define HTTP_STATUSES \
@@ -69,10 +75,7 @@ struct http_response
 #undef X
     } status;
 
-    struct http_header
-    {
-        char *header, *value;
-    } *headers;
+    struct http_header *headers;
 
     union
     {
@@ -96,6 +99,7 @@ struct http_cfg
         struct http_response *r, void *user);
     const char *tmpdir;
     void *user;
+    size_t max_headers;
 };
 
 struct http_ctx *http_alloc(const struct http_cfg *cfg);