Replace libfmt with std::format

.github/workflows/osrm-backend.yml

@@ -284,13 +284,13 @@ jobs:
             CXXCOMPILER: g++-13
             CXXFLAGS: '-Wno-array-bounds -Wno-uninitialized'
 
-          - name: gcc-12-release
+          - name: gcc-15-release
             continue-on-error: false
             node: 22
-            runs-on: ubuntu-22.04
+            runs-on: ubuntu-25.04
             BUILD_TYPE: Release
-            CCOMPILER: gcc-12
-            CXXCOMPILER: g++-12
+            CCOMPILER: gcc-15
+            CXXCOMPILER: g++-15
             CXXFLAGS: '-Wno-array-bounds -Wno-uninitialized'
 
           - name: conan-linux-release-node

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Unreleased
   - Changes from 6.0.0
     - Misc:
+      - CHANGED: Remove libfmt from third_party and replace with std::format [#7238](https://github.com/Project-OSRM/osrm-backend/issues/7238)
       - ADDED: Add husky pre-commit hook for compiling and linting staged JS files [#7228](https://github.com/Project-OSRM/osrm-backend/issues/7228)
       - CHANGED: Standardize linting configuration with ESM-specific rules [#7229](https://github.com/Project-OSRM/osrm-backend/issues/7229)
       - CHANGED: Convert scripts from CommonJS to modern ESM format [#7230](https://github.com/Project-OSRM/osrm-backend/pull/7230)

include/util/json_renderer.hpp

@@ -15,8 +15,6 @@
 
 #include <boost/assert.hpp>
 
-#include <fmt/compile.h>
-
 namespace osrm::util::json
 {
 
@@ -50,12 +48,16 @@ template <typename Out> struct Renderer
     {
         // we don't want to print NaN or Infinity
         BOOST_ASSERT(std::isfinite(number.value));
-        // `fmt::memory_buffer` stores first 500 bytes in the object itself(i.e. on stack in this
-        // case) and then grows using heap if needed
-        fmt::memory_buffer buffer;
-        fmt::format_to(std::back_inserter(buffer), FMT_COMPILE("{:.10g}"), number.value);
+        // 64 bytes is plenty for "{:.10g}" formatted doubles
+        std::array<char, 64> buffer{};
+
+        // format into the buffer
+        auto it = std::format_to(buffer.begin(), "{:.10g}", number.value);
+
+        // compute number of characters to write
+        const size_t size = static_cast<size_t>(std::distance(buffer.begin(), it));
 
-        write(buffer.data(), buffer.size());
+        write(buffer.data(), size);
     }
 
     void operator()(const Object &object)

scripts/update_dependencies.sh

@@ -27,9 +27,6 @@ PROTOZERO_TAG=v1.7.1
 VTZERO_PATH="mapbox/vtzero"
 VTZERO_TAG=v1.1.0
 
-FMT_PATH="fmtlib/fmt"
-FMT_TAG=v10.2.1
-
 FLATBUFFERS_PATH="google/flatbuffers"
 FLATBUFFERS_TAG=v24.3.25
 
@@ -56,6 +53,6 @@ function update_subtree () {
 }
 
 ## Update dependencies
-for dep in osmium sol rapidjson microtar protozero vtzero fmt flatbuffers; do
+for dep in osmium sol rapidjson microtar protozero vtzero flatbuffers; do
     update_subtree $dep
 done

src/server/connection.cpp

@@ -7,7 +7,7 @@
 #include <boost/iostreams/filter/gzip.hpp>
 #include <boost/iostreams/filtering_stream.hpp>
 
-#include <fmt/format.h>
+#include <format>
 #include <vector>
 
 namespace osrm::server
@@ -91,9 +91,9 @@ void Connection::handle_read(const boost::system::error_code &error, std::size_t
         {
             keep_alive = true;
             current_reply.headers.emplace_back("Connection", "keep-alive");
-            current_reply.headers.emplace_back("Keep-Alive",
-                                               "timeout=" + fmt::to_string(keepalive_timeout) +
-                                                   ", max=" + fmt::to_string(processed_requests));
+            current_reply.headers.emplace_back(
+                "Keep-Alive",
+                std::format("timeout={}, max={}", keepalive_timeout, processed_requests));
         }
 
         // compress the result w/ gzip/deflate if requested

src/util/log.cpp

@@ -1,8 +1,9 @@
 #include "util/log.hpp"
 #include "util/isatty.hpp"
 #include <boost/algorithm/string/predicate.hpp>
+#include <chrono>
 #include <cstdio>
-#include <fmt/chrono.h>
+#include <format>
 #include <iostream>
 #include <mutex>
 #include <string>
@@ -75,12 +76,13 @@ void Log::Init()
 
         auto format = [is_terminal](const char *level, const char *color)
         {
-            const auto timestamp = std::chrono::system_clock::now();
-            return fmt::format("{}[{:%FT%H:%M:}{:%S}] [{}] ",
-                               is_terminal ? color : "",
-                               timestamp,
-                               timestamp.time_since_epoch(),
-                               level);
+            const auto now = std::chrono::system_clock::now();
+
+            // Format full timestamp with seconds precision
+            // ISO-8601 style: 2025-09-13T15:42:07
+            const auto timestamp = std::format("{:%FT%T}", floor<std::chrono::seconds>(now));
+
+            return std::format("{}[{}] [{}] ", is_terminal ? color : "", timestamp, level);
         };
 
         switch (level)