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.

6 files changed, 132 insertions, 0 deletions

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;
+}