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.

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

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

examples/CMakeLists.txt

@@ -1,3 +1,4 @@
 cmake_minimum_required(VERSION 3.13)
+add_subdirectory(headers)
 add_subdirectory(hello)
 add_subdirectory(html)

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)
 

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)

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)

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.

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;
+}

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)

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)

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);

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);