net: http: Add compression support in HTTP server

Add compression support using the accept-encoding
header to the http server static filesystem resource.

Signed-off-by: Carlo Kirchmeier <carlo.kirchmeier@zuehlke.com>

include/zephyr/net/http/compression.h

@@ -0,0 +1,54 @@
+/** @file
+ * @brief HTTP compressions
+ */
+
+/*
+ * Copyright (c) 2025 Endress+Hauser
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_INCLUDE_NET_HTTP_COMPRESSION_H_
+#define ZEPHYR_INCLUDE_NET_HTTP_COMPRESSION_H_
+
+/**
+ * @brief HTTP compressions
+ * @defgroup http_compressions HTTP compressions
+ * @since 4.2
+ * @version 0.1.0
+ * @ingroup networking
+ * @{
+ */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <stdint.h>
+#include <stddef.h>
+
+#define HTTP_COMPRESSION_MAX_STRING_LEN 8
+
+/** @brief HTTP compressions */
+enum http_compression {
+	HTTP_GZIP = 0,     /**< GZIP */
+	HTTP_COMPRESS = 1, /**< COMPRESS */
+	HTTP_DEFLATE = 2,  /**< DEFLATE */
+	HTTP_BR = 3,       /**< BR */
+	HTTP_ZSTD = 4      /**< ZSTD */
+};
+
+void http_compression_parse_accept_encoding(const char *accept_encoding, size_t len,
+					    uint8_t *supported_compression);
+const char *http_compression_text(enum http_compression compression);
+int http_compression_from_text(enum http_compression compression[static 1], const char *text);
+
+#ifdef __cplusplus
+}
+#endif
+
+/**
+ * @}
+ */
+
+#endif /* ZEPHYR_INCLUDE_NET_HTTP_COMPRESSION_H_ */

include/zephyr/net/http/server.h

@@ -475,6 +475,11 @@ struct http_client_ctx {
 	IF_ENABLED(CONFIG_WEBSOCKET, (uint8_t ws_sec_key[HTTP_SERVER_WS_MAX_SEC_KEY_LEN]));
 /** @endcond */
 
+	/** @cond INTERNAL_HIDDEN */
+	/** Client supported compression. */
+	uint8_t supported_compression;
+	/** @endcond */
+
 	/** Flag indicating that HTTP2 preface was sent. */
 	bool preface_sent : 1;
 
@@ -493,6 +498,9 @@ struct http_client_ctx {
 	/** Flag indicating Websocket key is being processed. */
 	bool websocket_sec_key_next : 1;
 
+	/** Flag indicating accept encoding is being processed. */
+	bool accept_encoding_next: 1;
+
 	/** The next frame on the stream is expectd to be a continuation frame. */
 	bool expect_continuation : 1;
 };

subsys/net/lib/http/CMakeLists.txt

@@ -15,7 +15,8 @@ zephyr_library_sources_ifdef(CONFIG_HTTP_SERVER http_server_core.c
 						http_server_http1.c
 						http_server_http2.c
 						http_hpack.c
-						http_huffman.c)
+						http_huffman.c
+            http_compression.c)
 if(CONFIG_HTTP_SERVER AND CONFIG_WEBSOCKET)
   zephyr_library_sources(http_server_ws.c)
   zephyr_library_link_libraries_ifdef(CONFIG_MBEDTLS mbedTLS)

subsys/net/lib/http/headers/server_internal.h

@@ -15,6 +15,7 @@
 #include <zephyr/net/http/status.h>
 #include <zephyr/net/http/hpack.h>
 #include <zephyr/net/http/frame.h>
+#include <zephyr/net/http/compression.h>
 
 /* HTTP1/HTTP2 state handling */
 int handle_http_frame_rst_stream(struct http_client_ctx *client);
@@ -42,7 +43,9 @@ struct http_resource_detail *get_resource_detail(const struct http_service_desc
 int http_server_sendall(struct http_client_ctx *client, const void *buf, size_t len);
 void http_server_get_content_type_from_extension(char *url, char *content_type,
 						 size_t content_type_size);
-int http_server_find_file(char *fname, size_t fname_size, size_t *file_size, bool *gzipped);
+int http_server_find_file(char *fname, size_t fname_size, size_t *file_size,
+			  uint8_t supported_compression,
+			  enum http_compression *chosen_compression);
 void http_client_timer_restart(struct http_client_ctx *client);
 bool http_response_is_final(struct http_response_ctx *rsp, enum http_data_status status);
 bool http_response_is_provided(struct http_response_ctx *rsp);

subsys/net/lib/http/http_compression.c

@@ -0,0 +1,129 @@
+/** @file
+ * @brief HTTP compression handling functions
+ *
+ * Helper functions to handle compression formats
+ */
+
+/*
+ * Copyright (c) 2025 Endress+Hauser
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#include <assert.h>
+#include <stdbool.h>
+#include <string.h>
+#include <strings.h>
+
+#include <zephyr/net/http/compression.h>
+#include <zephyr/sys/util.h>
+
+static bool compression_value_is_valid(enum http_compression compression);
+static int http_compression_match(enum http_compression compression[static 1], const char *text,
+				  enum http_compression expected);
+
+void http_compression_parse_accept_encoding(const char *accept_encoding, size_t len,
+					    uint8_t *supported_compression)
+{
+	enum http_compression detected_compression;
+	char strbuf[HTTP_COMPRESSION_MAX_STRING_LEN + 1] = {0};
+	const char *start = accept_encoding;
+	const char *end = NULL;
+	bool priority_string = false;
+
+	*supported_compression = 0;
+	for (size_t i = 0; i < len; i++) {
+		if (accept_encoding[i] == 0) {
+			break;
+		} else if (accept_encoding[i] == ' ') {
+			start = &accept_encoding[i + 1];
+			continue;
+		} else if (accept_encoding[i] == ';') {
+			end = &accept_encoding[i];
+			priority_string = true;
+		} else if (accept_encoding[i] == ',') {
+			if (!priority_string) {
+				end = &accept_encoding[i];
+			}
+			priority_string = false;
+		} else if (i + 1 == len) {
+			end = &accept_encoding[i + 1];
+		}
+
+		if (end == NULL) {
+			continue;
+		}
+
+		if (end - start > HTTP_COMPRESSION_MAX_STRING_LEN) {
+			end = NULL;
+			start = end + 1;
+			continue;
+		}
+
+		memcpy(strbuf, start, end - start);
+		strbuf[end - start] = 0;
+
+		if (http_compression_from_text(&detected_compression, strbuf) == 0) {
+			WRITE_BIT(*supported_compression, detected_compression, true);
+		}
+
+		end = NULL;
+		start = end + 1;
+	}
+}
+
+const char *http_compression_text(enum http_compression compression)
+{
+	switch (compression) {
+	case HTTP_GZIP:
+		return "gzip";
+	case HTTP_COMPRESS:
+		return "compress";
+	case HTTP_DEFLATE:
+		return "deflate";
+	case HTTP_BR:
+		return "br";
+	case HTTP_ZSTD:
+		return "zstd";
+	}
+	return "";
+}
+
+int http_compression_from_text(enum http_compression compression[static 1], const char *text)
+{
+	assert(compression);
+	assert(text);
+
+	for (enum http_compression i = 0; compression_value_is_valid(i); ++i) {
+		if (http_compression_match(compression, text, i) == 0) {
+			return 0;
+		}
+	}
+	return 1;
+}
+
+static bool compression_value_is_valid(enum http_compression compression)
+{
+	switch (compression) {
+	case HTTP_GZIP:
+	case HTTP_COMPRESS:
+	case HTTP_DEFLATE:
+	case HTTP_BR:
+	case HTTP_ZSTD:
+		return true;
+	}
+	return false;
+}
+
+static int http_compression_match(enum http_compression compression[static 1], const char *text,
+				  enum http_compression expected)
+{
+	assert(compression);
+	assert(text);
+
+	if (strcasecmp(http_compression_text(expected), text) == 0) {
+		*compression = expected;
+		return 0;
+	} else {
+		return 1;
+	}
+}

subsys/net/lib/http/http_server_core.c

@@ -17,11 +17,13 @@
 #include <zephyr/kernel.h>
 #include <zephyr/logging/log.h>
 #include <zephyr/net/http/service.h>
+#include <zephyr/net/http/compression.h>
 #include <zephyr/net/net_ip.h>
 #include <zephyr/net/socket.h>
 #include <zephyr/net/tls_credentials.h>
 #include <zephyr/posix/sys/eventfd.h>
 #include <zephyr/posix/fnmatch.h>
+#include <zephyr/sys/util_macro.h>
 
 LOG_MODULE_REGISTER(net_http_server, CONFIG_NET_HTTP_SERVER_LOG_LEVEL);
 
@@ -785,26 +787,62 @@ struct http_resource_detail *get_resource_detail(const struct http_service_desc
 	return NULL;
 }
 
-int http_server_find_file(char *fname, size_t fname_size, size_t *file_size, bool *gzipped)
+int http_server_find_file(char *fname, size_t fname_size, size_t *file_size,
+			  uint8_t supported_compression, enum http_compression *chosen_compression)
 {
 	struct fs_dirent dirent;
 	size_t len;
 	int ret;
 
-	ret = fs_stat(fname, &dirent);
-	if (ret < 0) {
-		len = strlen(fname);
+	len = strlen(fname);
+	if (IS_BIT_SET(supported_compression, HTTP_BR)) {
+		snprintk(fname + len, fname_size - len, ".br");
+		ret = fs_stat(fname, &dirent);
+		if (ret == 0) {
+			*chosen_compression = HTTP_BR;
+			goto return_filename;
+		}
+	}
+	if (IS_BIT_SET(supported_compression, HTTP_GZIP)) {
 		snprintk(fname + len, fname_size - len, ".gz");
 		ret = fs_stat(fname, &dirent);
-		*gzipped = (ret == 0);
+		if (ret == 0) {
+			*chosen_compression = HTTP_GZIP;
+			goto return_filename;
+		}
 	}
-
-	if (ret == 0) {
-		*file_size = dirent.size;
-		return ret;
+	if (IS_BIT_SET(supported_compression, HTTP_ZSTD)) {
+		snprintk(fname + len, fname_size - len, ".zst");
+		ret = fs_stat(fname, &dirent);
+		if (ret == 0) {
+			*chosen_compression = HTTP_ZSTD;
+			goto return_filename;
+		}
+	}
+	if (IS_BIT_SET(supported_compression, HTTP_COMPRESS)) {
+		snprintk(fname + len, fname_size - len, ".lzw");
+		ret = fs_stat(fname, &dirent);
+		if (ret == 0) {
+			*chosen_compression = HTTP_COMPRESS;
+			goto return_filename;
+		}
+	}
+	if (IS_BIT_SET(supported_compression, HTTP_DEFLATE)) {
+		snprintk(fname + len, fname_size - len, ".zz");
+		ret = fs_stat(fname, &dirent);
+		if (ret == 0) {
+			*chosen_compression = HTTP_DEFLATE;
+			goto return_filename;
+		}
+	}
+	ret = fs_stat(fname, &dirent);
+	if (ret != 0) {
+		return -ENOENT;
 	}
 
-	return -ENOENT;
+return_filename:
+	*file_size = dirent.size;
+	return ret;
 }
 
 void http_server_get_content_type_from_extension(char *url, char *content_type,