[PLAT-7804] Improve crash report writing performance with buffered output

Bugsnag.xcodeproj/project.pbxproj

@@ -696,6 +696,9 @@
 		01B14C57251CE55F00118748 /* report-react-native-promise-rejection.json in Resources */ = {isa = PBXBuildFile; fileRef = 01B14C55251CE55F00118748 /* report-react-native-promise-rejection.json */; };
 		01B14C58251CE55F00118748 /* report-react-native-promise-rejection.json in Resources */ = {isa = PBXBuildFile; fileRef = 01B14C55251CE55F00118748 /* report-react-native-promise-rejection.json */; };
 		01B6BB7E25D5777F00FC4DE6 /* BugsnagSwiftPublicAPITests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 008966B02486D43500DC48C2 /* BugsnagSwiftPublicAPITests.swift */; };
+		01B74E9C27903326004B9765 /* BSG_KSFileTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 01B74E9B27903326004B9765 /* BSG_KSFileTests.m */; };
+		01B74E9D27903326004B9765 /* BSG_KSFileTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 01B74E9B27903326004B9765 /* BSG_KSFileTests.m */; };
+		01B74E9E27903326004B9765 /* BSG_KSFileTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 01B74E9B27903326004B9765 /* BSG_KSFileTests.m */; };
 		01B79DA9267CC4A000C8CC5E /* BSGUtils.h in Headers */ = {isa = PBXBuildFile; fileRef = 01B79DA7267CC4A000C8CC5E /* BSGUtils.h */; };
 		01B79DAA267CC4A000C8CC5E /* BSGUtils.h in Headers */ = {isa = PBXBuildFile; fileRef = 01B79DA7267CC4A000C8CC5E /* BSGUtils.h */; };
 		01B79DAB267CC4A000C8CC5E /* BSGUtils.h in Headers */ = {isa = PBXBuildFile; fileRef = 01B79DA7267CC4A000C8CC5E /* BSGUtils.h */; };
@@ -712,6 +715,13 @@
 		01C17AE72542ED7F00C102C9 /* KSCrashReportWriterTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 01C17AE62542ED7F00C102C9 /* KSCrashReportWriterTests.m */; };
 		01C17AE82542ED7F00C102C9 /* KSCrashReportWriterTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 01C17AE62542ED7F00C102C9 /* KSCrashReportWriterTests.m */; };
 		01C17AE92542ED7F00C102C9 /* KSCrashReportWriterTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 01C17AE62542ED7F00C102C9 /* KSCrashReportWriterTests.m */; };
+		01CB95BF278F0C830077744A /* BSG_KSFile.h in Headers */ = {isa = PBXBuildFile; fileRef = 01CB95BD278F0C830077744A /* BSG_KSFile.h */; };
+		01CB95C0278F0C830077744A /* BSG_KSFile.h in Headers */ = {isa = PBXBuildFile; fileRef = 01CB95BD278F0C830077744A /* BSG_KSFile.h */; };
+		01CB95C1278F0C830077744A /* BSG_KSFile.h in Headers */ = {isa = PBXBuildFile; fileRef = 01CB95BD278F0C830077744A /* BSG_KSFile.h */; };
+		01CB95C2278F0C830077744A /* BSG_KSFile.c in Sources */ = {isa = PBXBuildFile; fileRef = 01CB95BE278F0C830077744A /* BSG_KSFile.c */; };
+		01CB95C3278F0C830077744A /* BSG_KSFile.c in Sources */ = {isa = PBXBuildFile; fileRef = 01CB95BE278F0C830077744A /* BSG_KSFile.c */; };
+		01CB95C4278F0C830077744A /* BSG_KSFile.c in Sources */ = {isa = PBXBuildFile; fileRef = 01CB95BE278F0C830077744A /* BSG_KSFile.c */; };
+		01CB95C5278F0C830077744A /* BSG_KSFile.c in Sources */ = {isa = PBXBuildFile; fileRef = 01CB95BE278F0C830077744A /* BSG_KSFile.c */; };
 		01CCAEEA25D414D60057268D /* BugsnagLastRunInfo.h in Headers */ = {isa = PBXBuildFile; fileRef = 01CCAEE825D414D60057268D /* BugsnagLastRunInfo.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		01CCAEEB25D414D60057268D /* BugsnagLastRunInfo.h in Headers */ = {isa = PBXBuildFile; fileRef = 01CCAEE825D414D60057268D /* BugsnagLastRunInfo.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		01CCAEEC25D414D60057268D /* BugsnagLastRunInfo.h in Headers */ = {isa = PBXBuildFile; fileRef = 01CCAEE825D414D60057268D /* BugsnagLastRunInfo.h */; settings = {ATTRIBUTES = (Public, ); }; };
@@ -1378,13 +1388,16 @@
 		01A617842733D15C00024A0B /* BugsnagNetworkRequestPlugin.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; path = BugsnagNetworkRequestPlugin.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		01ABD8782786DF9A009A5CA2 /* BSG_KSCrashReportTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = BSG_KSCrashReportTests.m; sourceTree = "<group>"; };
 		01B14C55251CE55F00118748 /* report-react-native-promise-rejection.json */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.json; path = "report-react-native-promise-rejection.json"; sourceTree = "<group>"; };
+		01B74E9B27903326004B9765 /* BSG_KSFileTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = BSG_KSFileTests.m; sourceTree = "<group>"; };
 		01B79DA7267CC4A000C8CC5E /* BSGUtils.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = BSGUtils.h; sourceTree = "<group>"; };
 		01B79DA8267CC4A000C8CC5E /* BSGUtils.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = BSGUtils.m; sourceTree = "<group>"; };
 		01BDB1CE25DEBF4600A91FAF /* BSGEventUploadKSCrashReportOperationTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = BSGEventUploadKSCrashReportOperationTests.m; sourceTree = "<group>"; };
 		01BDB21425DEC02900A91FAF /* Data */ = {isa = PBXFileReference; lastKnownFileType = folder; path = Data; sourceTree = "<group>"; };
 		01C17AE62542ED7F00C102C9 /* KSCrashReportWriterTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = KSCrashReportWriterTests.m; sourceTree = "<group>"; };
 		01C2769B2601F44D006901EA /* CHANGELOG.md */ = {isa = PBXFileReference; lastKnownFileType = net.daringfireball.markdown; path = CHANGELOG.md; sourceTree = "<group>"; };
 		01C2769C2601F455006901EA /* CONTRIBUTING.md */ = {isa = PBXFileReference; lastKnownFileType = net.daringfireball.markdown; path = CONTRIBUTING.md; sourceTree = "<group>"; };
+		01CB95BD278F0C830077744A /* BSG_KSFile.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = BSG_KSFile.h; sourceTree = "<group>"; };
+		01CB95BE278F0C830077744A /* BSG_KSFile.c */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.c; path = BSG_KSFile.c; sourceTree = "<group>"; };
 		01CCAEE825D414D60057268D /* BugsnagLastRunInfo.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = BugsnagLastRunInfo.h; sourceTree = "<group>"; };
 		01CCAEE925D414D60057268D /* BugsnagLastRunInfo.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = BugsnagLastRunInfo.m; sourceTree = "<group>"; };
 		01CCAEFF25D4151C0057268D /* BugsnagLastRunInfo+Private.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = "BugsnagLastRunInfo+Private.h"; sourceTree = "<group>"; };
@@ -1535,6 +1548,7 @@
 			isa = PBXGroup;
 			children = (
 				01ABD8782786DF9A009A5CA2 /* BSG_KSCrashReportTests.m */,
+				01B74E9B27903326004B9765 /* BSG_KSFileTests.m */,
 				008966D82486D43700DC48C2 /* BSG_KSMachHeadersTests.m */,
 				008966EA2486D43700DC48C2 /* BSG_KSMachTests.m */,
 				008966D62486D43700DC48C2 /* FileBasedTestCase.h */,
@@ -1628,6 +1642,8 @@
 				008969292486DAD000DC48C2 /* BSG_KSCrashState.m */,
 				0089692B2486DAD000DC48C2 /* BSG_KSCrashType.c */,
 				008969482486DAD000DC48C2 /* BSG_KSCrashType.h */,
+				01CB95BE278F0C830077744A /* BSG_KSFile.c */,
+				01CB95BD278F0C830077744A /* BSG_KSFile.h */,
 				0089692F2486DAD000DC48C2 /* BSG_KSSystemInfo.h */,
 				0089694C2486DAD000DC48C2 /* BSG_KSSystemInfo.m */,
 				008969312486DAD000DC48C2 /* BSG_KSSystemInfoC.h */,
@@ -2146,6 +2162,7 @@
 				010FF28425ED2A8D00E4F2B0 /* BSGAppHangDetector.h in Headers */,
 				008967F42486DA4500DC48C2 /* BSGSessionUploader.h in Headers */,
 				0126DF1B257A92860031A70C /* BugsnagSession+Private.h in Headers */,
+				01CB95BF278F0C830077744A /* BSG_KSFile.h in Headers */,
 				008969E12486DAD100DC48C2 /* BSG_KSSystemInfo.h in Headers */,
 				00896A0E2486DAD100DC48C2 /* BSG_KSCrashSentry.h in Headers */,
 				008969D22486DAD100DC48C2 /* BSG_KSCrashContext.h in Headers */,
@@ -2252,6 +2269,7 @@
 				008967F52486DA4500DC48C2 /* BSGSessionUploader.h in Headers */,
 				010FF28525ED2A8D00E4F2B0 /* BSGAppHangDetector.h in Headers */,
 				008969E22486DAD100DC48C2 /* BSG_KSSystemInfo.h in Headers */,
+				01CB95C0278F0C830077744A /* BSG_KSFile.h in Headers */,
 				0126DF1C257A92860031A70C /* BugsnagSession+Private.h in Headers */,
 				00896A0F2486DAD100DC48C2 /* BSG_KSCrashSentry.h in Headers */,
 				008969D32486DAD100DC48C2 /* BSG_KSCrashContext.h in Headers */,
@@ -2358,6 +2376,7 @@
 				008967F62486DA4500DC48C2 /* BSGSessionUploader.h in Headers */,
 				010FF28625ED2A8D00E4F2B0 /* BSGAppHangDetector.h in Headers */,
 				008969E32486DAD100DC48C2 /* BSG_KSSystemInfo.h in Headers */,
+				01CB95C1278F0C830077744A /* BSG_KSFile.h in Headers */,
 				0126DF1D257A92860031A70C /* BugsnagSession+Private.h in Headers */,
 				00896A102486DAD100DC48C2 /* BSG_KSCrashSentry.h in Headers */,
 				008969D42486DAD100DC48C2 /* BSG_KSCrashContext.h in Headers */,
@@ -2741,6 +2760,7 @@
 				01840B7225DC26E200F95648 /* BSGEventUploader.m in Sources */,
 				008968C32486DA9600DC48C2 /* BugsnagUser.m in Sources */,
 				CBAB4DD82510D2460092CBAA /* BugsnagKVStoreObjC.m in Sources */,
+				01CB95C2278F0C830077744A /* BSG_KSFile.c in Sources */,
 				008968A72486DA9600DC48C2 /* BugsnagSession.m in Sources */,
 				0089683A2486DA6C00DC48C2 /* BugsnagMetadata.m in Sources */,
 				013D9CD426C5262F0077F0AD /* UISceneStub.m in Sources */,
@@ -2844,6 +2864,7 @@
 				008967752486D43700DC48C2 /* XCTestCase+KSCrash.m in Sources */,
 				CB9103642502320A00E9D1E2 /* BugsnagApiClientTest.m in Sources */,
 				008967602486D43700DC48C2 /* BugsnagBreadcrumbsTest.m in Sources */,
+				01B74E9C27903326004B9765 /* BSG_KSFileTests.m in Sources */,
 				CB10E53F250BA8DE00AF5824 /* BugsnagKVStoreTest.m in Sources */,
 				CB6419AB25A73E8C00613D25 /* BSGStorageMigratorTests.m in Sources */,
 				E701FAA72490EF77008D842F /* ClientApiValidationTest.m in Sources */,
@@ -2898,6 +2919,7 @@
 				008968BA2486DA9600DC48C2 /* BugsnagStacktrace.m in Sources */,
 				00896A152486DAD100DC48C2 /* BSG_KSCrashSentry_Signal.c in Sources */,
 				01468F5625876DC1002B0519 /* BSGNotificationBreadcrumbs.m in Sources */,
+				01CB95C3278F0C830077744A /* BSG_KSFile.c in Sources */,
 				008967BF2486DA1900DC48C2 /* BugsnagClient.m in Sources */,
 				008968962486DA9600DC48C2 /* BugsnagHandledState.m in Sources */,
 				008969C42486DAD100DC48C2 /* BSG_KSObjC.c in Sources */,
@@ -3009,6 +3031,7 @@
 				008967A02486D43700DC48C2 /* KSCrashSentry_Tests.m in Sources */,
 				008967432486D43700DC48C2 /* BugsnagSessionTrackerStopTest.m in Sources */,
 				008967972486D43700DC48C2 /* KSCrashState_Tests.m in Sources */,
+				01B74E9D27903326004B9765 /* BSG_KSFileTests.m in Sources */,
 				008967762486D43700DC48C2 /* XCTestCase+KSCrash.m in Sources */,
 				01E8765F256684E700F4B70A /* URLSessionMock.m in Sources */,
 				008967312486D43700DC48C2 /* BSGClientObserverTests.m in Sources */,
@@ -3088,6 +3111,7 @@
 				01840B7425DC26E200F95648 /* BSGEventUploader.m in Sources */,
 				008968C52486DA9600DC48C2 /* BugsnagUser.m in Sources */,
 				CBAB4DDA2510D2460092CBAA /* BugsnagKVStoreObjC.m in Sources */,
+				01CB95C4278F0C830077744A /* BSG_KSFile.c in Sources */,
 				008968A92486DA9600DC48C2 /* BugsnagSession.m in Sources */,
 				0089683C2486DA6C00DC48C2 /* BugsnagMetadata.m in Sources */,
 				013D9CD626C5262F0077F0AD /* UISceneStub.m in Sources */,
@@ -3182,6 +3206,7 @@
 				008967322486D43700DC48C2 /* BSGClientObserverTests.m in Sources */,
 				CBA2249D251E429C00B87416 /* TestSupport.m in Sources */,
 				01847DAE26441A5E00ADA4C7 /* BSGInternalErrorReporterTests.m in Sources */,
+				01B74E9E27903326004B9765 /* BSG_KSFileTests.m in Sources */,
 				004E35372487AFF2007FBAE4 /* BugsnagHandledStateTest.m in Sources */,
 				016875C8258D003200DFFF69 /* NSUserDefaultsStub.m in Sources */,
 				01935AE3275E68E9007498B3 /* UIApplicationStub.m in Sources */,
@@ -3261,6 +3286,7 @@
 				008967DD2486DA2D00DC48C2 /* BugsnagConfiguration.m in Sources */,
 				008968E42486DAA700DC48C2 /* BugsnagPluginClient.m in Sources */,
 				01840B7525DC26E200F95648 /* BSGEventUploader.m in Sources */,
+				01CB95C5278F0C830077744A /* BSG_KSFile.c in Sources */,
 				008968BC2486DA9600DC48C2 /* BugsnagStacktrace.m in Sources */,
 				008968242486DA5600DC48C2 /* BugsnagKeys.m in Sources */,
 				008967B72486D9D800DC48C2 /* BugsnagBreadcrumbs.m in Sources */,

Bugsnag.xcodeproj/xcshareddata/xcbaselines/00AD1C7A24869B0E00A27979.xcbaseline/B9A70F85-2A05-489B-A5BA-1129C478B0A1.plist

@@ -11,7 +11,7 @@
 				<key>com.apple.XCTPerformanceMetric_WallClockTime</key>
 				<dict>
 					<key>baselineAverage</key>
-					<real>0.065700</real>
+					<real>0.034600</real>
 					<key>baselineIntegrationDisplayName</key>
 					<string>Local Baseline</string>
 				</dict>

Bugsnag.xcodeproj/xcshareddata/xcbaselines/00AD1C7A24869B0E00A27979.xcbaseline/D90C8D39-16DA-4CCB-8283-66F4A3B10BA2.plist

@@ -11,7 +11,7 @@
 				<key>com.apple.XCTPerformanceMetric_WallClockTime</key>
 				<dict>
 					<key>baselineAverage</key>
-					<real>0.468000</real>
+					<real>0.195000</real>
 					<key>baselineIntegrationDisplayName</key>
 					<string>Local Baseline</string>
 				</dict>

Bugsnag.xcodeproj/xcshareddata/xcbaselines/00AD1CB424869C1200A27979.xcbaseline/7E1A1286-DD8C-4E45-9E88-4335CD976176.plist

@@ -11,7 +11,7 @@
 				<key>com.apple.XCTPerformanceMetric_WallClockTime</key>
 				<dict>
 					<key>baselineAverage</key>
-					<real>0.091900</real>
+					<real>0.042200</real>
 					<key>baselineIntegrationDisplayName</key>
 					<string>Local Baseline</string>
 				</dict>

Bugsnag/KSCrash/Source/KSCrash/Recording/BSG_KSCrashReport.c

@@ -29,6 +29,7 @@
 #include "BSG_KSBacktrace_Private.h"
 #include "BSG_KSCrashReportFields.h"
 #include "BSG_KSCrashReportVersion.h"
+#include "BSG_KSFile.h"
 #include "BSG_KSFileUtils.h"
 #include "BSG_KSJSONCodec.h"
 #include "BSG_KSMach.h"
@@ -308,8 +309,7 @@ void bsg_kscrw_i_endContainer(const BSG_KSCrashReportWriter *const writer) {
 
 int bsg_kscrw_i_addJSONData(const char *const data, const size_t length,
                             void *const userData) {
-    const int fd = *((int *)userData);
-    const bool success = bsg_ksfuwriteBytesToFD(fd, data, (ssize_t)length);
+    bool success = BSG_KSFileWrite(userData, data, length);
     return success ? BSG_KSJSON_OK : BSG_KSJSON_ERROR_CANNOT_ADD_DATA;
 }
 
@@ -1502,14 +1502,18 @@ void bsg_kscrashreport_writeMinimalReport(
 
     bsg_kscrw_i_updateStackOverflowStatus(crashContext);
 
+    BSG_KSFile file;
+    char buffer[512];
+    BSG_KSFileInit(&file, fd, buffer, sizeof(buffer) / sizeof(*buffer));
+
     BSG_KSJSONEncodeContext jsonContext;
-    jsonContext.userData = &fd;
+    jsonContext.userData = &file;
     BSG_KSCrashReportWriter concreteWriter;
     BSG_KSCrashReportWriter *writer = &concreteWriter;
     bsg_kscrw_i_prepareReportWriter(writer, &jsonContext);
 
     bsg_ksjsonbeginEncode(bsg_getJsonContext(writer), false,
-                          bsg_kscrw_i_addJSONData, &fd);
+                          bsg_kscrw_i_addJSONData, &file);
 
     writer->beginObject(writer, BSG_KSCrashField_Report);
     {
@@ -1541,6 +1545,7 @@ void bsg_kscrashreport_writeMinimalReport(
 
     bsg_ksjsonendEncode(bsg_getJsonContext(writer));
 
+    BSG_KSFileFlush(&file);
     close(fd);
 }
 
@@ -1557,14 +1562,18 @@ void bsg_kscrashreport_writeStandardReport(
 
     bsg_kscrw_i_updateStackOverflowStatus(crashContext);
 
+    BSG_KSFile file;
+    char buffer[4096];
+    BSG_KSFileInit(&file, fd, buffer, sizeof(buffer) / sizeof(*buffer));
+
     BSG_KSJSONEncodeContext jsonContext;
-    jsonContext.userData = &fd;
+    jsonContext.userData = &file;
     BSG_KSCrashReportWriter concreteWriter;
     BSG_KSCrashReportWriter *writer = &concreteWriter;
     bsg_kscrw_i_prepareReportWriter(writer, &jsonContext);
 
     bsg_ksjsonbeginEncode(bsg_getJsonContext(writer), false,
-                          bsg_kscrw_i_addJSONData, &fd);
+                          bsg_kscrw_i_addJSONData, &file);
 
     writer->beginObject(writer, BSG_KSCrashField_Report);
     {
@@ -1588,6 +1597,7 @@ void bsg_kscrashreport_writeStandardReport(
 
     bsg_ksjsonendEncode(bsg_getJsonContext(writer));
 
+    BSG_KSFileFlush(&file);
     close(fd);
 }
 

Bugsnag/KSCrash/Source/KSCrash/Recording/BSG_KSCrashState.m

@@ -26,7 +26,7 @@
 
 #include "BSG_KSCrashState.h"
 
-#include "BSG_KSFileUtils.h"
+#include "BSG_KSFile.h"
 #include "BSG_KSJSONCodec.h"
 #include "BSG_KSJSONCodecObjC.h"
 #include "BSG_KSMach.h"
@@ -154,8 +154,7 @@ int bsg_kscrashstate_i_onEndData(__unused void *const userData) {
  */
 int bsg_kscrashstate_i_addJSONData(const char *const data, const size_t length,
                                    void *const userData) {
-    const int fd = *((int *)userData);
-    const bool success = bsg_ksfuwriteBytesToFD(fd, data, (ssize_t)length);
+    bool success = BSG_KSFileWrite(userData, data, length);
     return success ? BSG_KSJSON_OK : BSG_KSJSON_ERROR_CANNOT_ADD_DATA;
 }
 
@@ -227,9 +226,13 @@ bool bsg_kscrashstate_i_saveState(const BSG_KSCrash_State *const state,
         return false;
     }
 
+    BSG_KSFile file;
+    char buffer[256];
+    BSG_KSFileInit(&file, fd, buffer, sizeof(buffer) / sizeof(*buffer));
+
     BSG_KSJSONEncodeContext JSONContext;
     bsg_ksjsonbeginEncode(&JSONContext, false, bsg_kscrashstate_i_addJSONData,
-                          &fd);
+                          &file);
 
     int result;
     if ((result = bsg_ksjsonbeginObject(&JSONContext, NULL)) != BSG_KSJSON_OK) {
@@ -269,6 +272,7 @@ bool bsg_kscrashstate_i_saveState(const BSG_KSCrash_State *const state,
     result = bsg_ksjsonendEncode(&JSONContext);
 
 done:
+    BSG_KSFileFlush(&file);
     close(fd);
 
     if (result != BSG_KSJSON_OK) {

Bugsnag/KSCrash/Source/KSCrash/Recording/BSG_KSFile.c

@@ -0,0 +1,59 @@
+//
+//  BSG_KSFile.c
+//  Bugsnag
+//
+//  Created by Nick Dowell on 12/01/2022.
+//  Copyright © 2022 Bugsnag Inc. All rights reserved.
+//
+
+#include "BSG_KSFile.h"
+
+#include "BSG_KSFileUtils.h"
+
+#include <string.h>
+#include <sys/param.h>
+
+static inline bool bsg_write(const int fd, const char *bytes, size_t length) {
+    return bsg_ksfuwriteBytesToFD(fd, bytes, (ssize_t)length);
+}
+
+void BSG_KSFileInit(BSG_KSFile *file, int fd, char *buffer, size_t length) {
+    file->fd = fd;
+    file->buffer = buffer;
+    file->bufferSize = length;
+    file->bufferUsed = 0;
+}
+
+bool BSG_KSFileWrite(BSG_KSFile *file, const char *data, size_t length) {
+    const size_t bytesCopied = MIN(file->bufferSize - file->bufferUsed, length);
+    memcpy(file->buffer + file->bufferUsed, data, bytesCopied);
+    file->bufferUsed += bytesCopied;
+    data += bytesCopied;
+    length -= bytesCopied;
+
+    if (file->bufferUsed == file->bufferSize) {
+        if (!BSG_KSFileFlush(file)) {
+            return false;
+        }
+    }
+
+    if (!length) {
+        return true;
+    }
+
+    if (length >= file->bufferSize) {
+        return bsg_write(file->fd, data, length);
+    }
+
+    memcpy(file->buffer, data, length);
+    file->bufferUsed = length;
+    return true;
+}
+
+bool BSG_KSFileFlush(BSG_KSFile *file) {
+    if (!bsg_write(file->fd, file->buffer, file->bufferUsed)) {
+        return false;
+    }
+    file->bufferUsed = 0;
+    return true;
+}

Bugsnag/KSCrash/Source/KSCrash/Recording/BSG_KSFile.h

@@ -0,0 +1,25 @@
+//
+//  BSG_KSFile.h
+//  Bugsnag
+//
+//  Created by Nick Dowell on 12/01/2022.
+//  Copyright © 2022 Bugsnag Inc. All rights reserved.
+//
+
+#pragma once
+
+#include <stdbool.h>
+#include <stddef.h>
+
+typedef struct {
+    int fd;
+    char *buffer;
+    size_t bufferSize;
+    size_t bufferUsed;
+} BSG_KSFile;
+
+void BSG_KSFileInit(BSG_KSFile *file, int fd, char *buffer, size_t length);
+
+bool BSG_KSFileWrite(BSG_KSFile *file, const char *data, size_t length);
+
+bool BSG_KSFileFlush(BSG_KSFile *file);

CHANGELOG.md

@@ -1,6 +1,13 @@
 Changelog
 =========
 
+## TBD
+
+### Bug fixes
+
+* Improve crash report writing performance with buffered output.
+  [#1281](https://github.com/bugsnag/bugsnag-cocoa/pull/1281)
+
 ## 6.16.0 (2022-01-12)
 
 ### Enhancements