Merge remote-tracking branch 'origin/feat/rsync-stderr-mode' into dev

# Conflicts:
#	RSYNC_COMPAT.md
#	src/shared/log.c
#	src/shared/log.h
#	tests/test_client_cli.c

RSYNC_COMPAT.md

@@ -7,10 +7,10 @@ This document maps rsync's full feature set to FastSync's current implementation
 | Status | Count | Description |
 |--------|-------|-------------|
 | ✅ Implemented | 35 | Feature works end-to-end |
-| 🔀 Alt Arg | 3 | Functionality exists but under different flag/semantics |
-| ⚠️ Partial | 1 | Flag parsed/stored but behavior incomplete |
-| ❌ Not Implemented | 98 | Flag not recognized or no behavior |
-| **Total** | **137** | |
+| 🔀 Alt Arg | 4 | Functionality exists but under different flag/semantics |
+| ⚠️ Partial | 5 | Flag parsed/stored but behavior incomplete |
+| ❌ Not Implemented | 97 | Flag not recognized or no behavior |
+| **Total** | **141** | |
 
 ---
 
@@ -25,7 +25,7 @@ This document maps rsync's full feature set to FastSync's current implementation
 | `-V`, `--version` | Print version | ✅ Implemented | |
 | `--info=FLAGS` | Fine-grained info verbosity | ❌ Not Implemented | Removed because it had no effect |
 | `--debug=FLAGS` | Fine-grained debug verbosity | ❌ Not Implemented | Removed because it had no effect |
-| `--stderr=MODE` | Change stderr output mode | ❌ Not Implemented | |
+| `--stderr=MODE` | Change stderr output mode | ⚠️ Partial | `errors` (default) and `all` are supported; `client` is rejected because FastSync has no rsync message channel |
 | `--no-motd` | Suppress daemon MOTD | ❌ Not Implemented | |
 | `--exclude=PATTERN` | Exclude files matching pattern | ✅ Implemented | Glob matching in scanner |
 | `--include=PATTERN` | Include files matching pattern | ✅ Implemented | Glob matching in scanner |
@@ -248,12 +248,11 @@ Ranked by user demand, implementation complexity, and interoperability impact:
 | 2 | `--ignore-times` / `-I` | Low | Medium — useful for forcing re-transfer |
 | 3 | `--size-only` | Low | Medium — common migration scenario |
 | 4 | `--existing` / `--ignore-existing` | Low | Medium — common sync patterns |
-| 5 | `--remove-source-files` | Low | High — common for moves/backup |
-| 6 | `--delete-during` | Medium | High — performance improvement |
-| 7 | `--delay-updates` | Medium | High — atomic updates |
-| 8 | `--chmod` | Low | Medium — permission flexibility |
-| 9 | `--executability` / `-E` | Low | Low — simple flag |
-| 10 | `--skip-compress` | Low | Medium — performance tuning |
+| 5 | `--delete-during` | Medium | High — performance improvement |
+| 6 | `--delay-updates` | Medium | High — atomic updates |
+| 7 | `--chmod` | Low | Medium — permission flexibility |
+| 8 | `--executability` / `-E` | Low | Low — simple flag |
+| 9 | `--skip-compress` | Low | Medium — performance tuning |
 
 ---
 

src/client/client_cli.c

@@ -86,6 +86,22 @@ static int set_nonneg_int_option(int* dest, const char* value, const char* optio
   return 0;
 }
 
+static int set_stderr_mode(const char* value) {
+  if (strcmp(value, "errors") == 0 || strcmp(value, "e") == 0)
+    log_set_stderr_mode(LOG_STDERR_ERRORS);
+  else if (strcmp(value, "all") == 0 || strcmp(value, "a") == 0)
+    log_set_stderr_mode(LOG_STDERR_ALL);
+  else if (strcmp(value, "client") == 0 || strcmp(value, "c") == 0) {
+    log_message(LOG_LEVEL_ERROR,
+                "--stderr=client is not supported: FastSync has no client message channel");
+    return -1;
+  } else {
+    log_message(LOG_LEVEL_ERROR, "--stderr must be errors or all");
+    return -1;
+  }
+  return 0;
+}
+
 static int read_patterns_from_file(const char* filepath, char*** patterns, int* count);
 
 /* Parse a string as an unsigned long long. Returns 0 on success, -1 on error. */
@@ -355,6 +371,12 @@ int parse_args(Config* config, int argc, char* argv[], int* positional_args,
       }
       config->log_file = lf;
       log_set_file(lf);
+    } else if (strncmp(argv[i], "--stderr=", 9) == 0) {
+      if (set_stderr_mode(argv[i] + 9) != 0)
+        return -1;
+    } else if (opt_is(argv[i], "--stderr", NULL)) {
+      if (i + 1 >= argc || set_stderr_mode(argv[++i]) != 0)
+        return -1;
     } else if (opt_is(argv[i], "--exclude-from", NULL) && i + 1 < argc) {
       if (read_patterns_from_file(argv[++i], &config->exclude_patterns, &config->exclude_count) !=
           0)

src/client/usage.c

@@ -62,6 +62,7 @@ void print_usage(void) {
   printf("  -h, --human-readable  Print byte sizes in human-readable form\n");
   printf("  --max-depth <n>     Maximum directory depth (0=unlimited)\n");
   printf("  --log-file <path>   Write log messages to file\n");
+  printf("  --stderr=MODE       Route logging to stderr: errors or all\n");
   printf("  --partial           Keep partial files on interrupted transfer\n");
   printf("  --partial-dir <dir> Directory for partial files\n");
   printf("  --fastsync-server-path <path>\n");

src/shared/log.c

@@ -9,6 +9,7 @@ static const char* log_level_strings[] = {"DEBUG", "INFO", "WARN", "ERROR"};
 static LogLevel current_log_level = LOG_LEVEL_WARNING;
 static FILE* log_fp = NULL;
 static _Thread_local bool eight_bit_output;
+static LogStderrMode stderr_mode = LOG_STDERR_ERRORS;
 
 void set_log_level(LogLevel level) {
   current_log_level = level;
@@ -26,6 +27,14 @@ bool log_get_8_bit_output(void) {
   return eight_bit_output;
 }
 
+void log_set_stderr_mode(LogStderrMode mode) {
+  stderr_mode = mode;
+}
+
+LogStderrMode log_get_stderr_mode(void) {
+  return stderr_mode;
+}
+
 static inline void write_message(FILE* dest_io, LogLevel log_level, struct tm t, const char* format,
                                  va_list args) {
   fprintf(dest_io, "%04d-%02d-%02d %02d:%02d:%02d [%s]: ", t.tm_year + 1900, t.tm_mon + 1,
@@ -46,7 +55,7 @@ void log_message(LogLevel log_level, const char* format, ...) {
     return;
 
   FILE* dest_io = stdout;
-  if (log_level == LOG_LEVEL_ERROR) {
+  if (stderr_mode == LOG_STDERR_ALL || log_level == LOG_LEVEL_ERROR) {
     dest_io = stderr;
   }
 

src/shared/log.h

@@ -5,6 +5,7 @@
 #include <stdbool.h>
 
 typedef enum { LOG_LEVEL_DEBUG, LOG_LEVEL_INFO, LOG_LEVEL_WARNING, LOG_LEVEL_ERROR } LogLevel;
+typedef enum { LOG_STDERR_ERRORS, LOG_STDERR_ALL } LogStderrMode;
 
 void log_message(LogLevel log_level, const char* message, ...);
 void log_perror(const char* context);
@@ -12,5 +13,7 @@ void set_log_level(LogLevel level);
 void log_set_file(FILE* fp);
 void log_set_8_bit_output(bool enabled);
 bool log_get_8_bit_output(void);
+void log_set_stderr_mode(LogStderrMode mode);
+LogStderrMode log_get_stderr_mode(void);
 
 #endif

tests/test_client_cli.c

@@ -1,6 +1,7 @@
 #include "test_client_cli.h"
 #include "client_validation.h"
 #include "config.h"
+#include "log.h"
 #include "test_utils.h"
 #include "utils.h"
 #include <stdlib.h>
@@ -415,6 +416,39 @@ static void test_parse_args_8_bit_output() {
   config_delete(cfg);
 }
 
+static void test_parse_args_stderr_modes() {
+  static const char* const modes[] = {"errors", "all", "e", "a"};
+  static const LogStderrMode expected[] = {LOG_STDERR_ERRORS, LOG_STDERR_ALL, LOG_STDERR_ERRORS,
+                                           LOG_STDERR_ALL};
+  for (size_t i = 0; i < sizeof(modes) / sizeof(modes[0]); i++) {
+    Config* cfg = config_create();
+    char option[32];
+    snprintf(option, sizeof(option), "--stderr=%s", modes[i]);
+    char* argv[] = {"fastsync", option, "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+    EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+    EXPECT_EQ_INT(log_get_stderr_mode(), expected[i]);
+    config_delete(cfg);
+  }
+  log_set_stderr_mode(LOG_STDERR_ERRORS);
+}
+
+static void test_parse_args_rejects_unsupported_stderr_modes() {
+  static const char* const modes[] = {"client", "c", "invalid"};
+  for (size_t i = 0; i < sizeof(modes) / sizeof(modes[0]); i++) {
+    Config* cfg = config_create();
+    char option[32];
+    snprintf(option, sizeof(option), "--stderr=%s", modes[i]);
+    char* argv[] = {"fastsync", option, "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+    EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), -1);
+    config_delete(cfg);
+  }
+  log_set_stderr_mode(LOG_STDERR_ERRORS);
+}
+
 void test_client_cli() {
   test_validate_config_required_paths();
   test_validate_config_incompatible_options();
@@ -442,4 +476,6 @@ void test_client_cli() {
   test_parse_args_archive();
   test_parse_args_fsync();
   test_parse_args_8_bit_output();
+  test_parse_args_stderr_modes();
+  test_parse_args_rejects_unsupported_stderr_modes();
 }

tests/test_log.c

@@ -1,6 +1,8 @@
 #include "test_log.h"
 #include "log.h"
 #include "test_utils.h"
+#include <string.h>
+#include <unistd.h>
 
 /* Test default log level: WARNING and ERROR should print, DEBUG and INFO should not.
  * We can't easily capture stderr in unit tests, so we verify the functions don't crash
@@ -90,6 +92,29 @@ static void test_log_filtering() {
   EXPECT_TRUE(true);
 }
 
+static void test_log_stderr_mode_all() {
+  int pipe_fds[2];
+  EXPECT_EQ_INT(pipe(pipe_fds), 0);
+  int saved_stderr = dup(STDERR_FILENO);
+  EXPECT_TRUE(saved_stderr >= 0);
+  EXPECT_TRUE(dup2(pipe_fds[1], STDERR_FILENO) >= 0);
+  close(pipe_fds[1]);
+
+  set_log_level(LOG_LEVEL_WARNING);
+  log_set_stderr_mode(LOG_STDERR_ALL);
+  log_message(LOG_LEVEL_WARNING, "warning routed to stderr");
+  fflush(stderr);
+
+  EXPECT_TRUE(dup2(saved_stderr, STDERR_FILENO) >= 0);
+  close(saved_stderr);
+  char output[128] = {0};
+  ssize_t length = read(pipe_fds[0], output, sizeof(output) - 1);
+  close(pipe_fds[0]);
+  EXPECT_TRUE(length > 0);
+  EXPECT_TRUE(strstr(output, "warning routed to stderr") != NULL);
+  log_set_stderr_mode(LOG_STDERR_ERRORS);
+}
+
 /* Test that log_message handles various format strings */
 static void test_log_message_formats() {
   set_log_level(LOG_LEVEL_DEBUG);
@@ -112,5 +137,6 @@ void test_log() {
   test_log_set_level_info();
   test_log_set_level_error();
   test_log_filtering();
+  test_log_stderr_mode_all();
   test_log_message_formats();
 }