Memory Buffer Logging

Data Structures
struct	LogMembufData

Typedefs
typedef struct LogMembufData	LogMembufData

Functions
LogDest *	logmembufRegister (int maxlevel, strref chanfilter, uint32 size, LogSerializer *ser)
LogMembufData *	logmembufData (LogDest *dest)
LogMembufData *	logmembufCreate (uint32 size, LogSerializer *ser)
void	logmembufMsgFunc (const LogRecord *rec, void *userdata)
void	logmembufCloseFunc (void *userdata)

Detailed Description

Memory buffer logging destination that writes log messages to a fixed-size circular buffer in memory. Useful for debugging, testing, and capturing logs in memory-constrained environments. When the buffer fills, new messages wrap around and overwrite the oldest entries.

Basic Usage:

// Register a 4KB buffer with the default compact text serializer
LogDest *dest = logmembufRegister(LOG_Debug, NULL, 4096, NULL);
 
// Log some messages
logStr(Info, _SL("Test message"));
logFlush();
 
// Access the buffer contents directly
LogMembufData *lmd = logmembufData(dest);
printf("Buffered logs:\n%.*s\n", (int)lmd->cur, lmd->buf);
 
// Cleanup -- this frees the buffer, so lmd is invalid afterwards
logUnregisterDest(dest);

Typedef Documentation

LogMembufData

typedef struct LogMembufData LogMembufData

Memory buffer log destination state

Contains the circular buffer and current write position. When cur reaches size, new messages wrap to the beginning. The buffer is null-terminated when possible.

Function Documentation

logmembufCloseFunc()

void logmembufCloseFunc

(

void *

userdata

)

Cleanup callback for memory buffer destinations

Frees the buffer and releases resources.

Parameters

userdata

LogMembufData pointer from logmembufCreate()

logmembufCreate()

LogMembufData * logmembufCreate	(	uint32	size,
		LogSerializer *	ser
	)

Create a memory buffer log destination

Only needed to register the buffer by hand with logRegisterDest() – logmembufRegister() does this and the registration together. The returned handle belongs to exactly one destination: it is freed by logmembufCloseFunc() and cannot be registered twice.

Parameters

size	Buffer size in bytes
ser	Serializer to render records with; ownership transfers. NULL gets a compact text serializer: short levels, bracketed channels, second-resolution timestamps.

Returns

Memory buffer handle

LogMembufData *lmd = logmembufCreate(8192, NULL);
LogDest *dest = logRegisterDest(LOG_Debug, NULL, logmembufMsgFunc, NULL,
                                logmembufCloseFunc, lmd);

logmembufData()

LogMembufData * logmembufData

(

LogDest *

dest

)

Get the buffer behind a memory buffer destination

The returned struct is owned by the destination and lives exactly as long as it does: logUnregisterDest() frees the buffer, so nothing may read it afterwards.

Reading cur races with the drain thread, which may be appending while this runs. Read it once into a local and use that for both the length and any copy – reading it twice lets it grow in between.

Parameters

dest	Destination handle from logmembufRegister()

Returns

Buffer state, or NULL if dest is not a memory buffer destination

LogDest *dest = logmembufRegister(LOG_Debug, NULL, 4096, NULL);
logFlush();
 
LogMembufData *lmd = logmembufData(dest);
uint32 cur = lmd->cur;
printf("%.*s", (int)cur, lmd->buf);

logmembufMsgFunc()

void logmembufMsgFunc	(	const LogRecord *	rec,
		void *	userdata
	)

Log message callback for memory buffer destinations

Serializes a log record and appends it to the circular buffer, newline-terminated.

Parameters

rec	Log record to write
userdata	LogMembufData pointer from logmembufCreate()

logmembufRegister()

LogDest * logmembufRegister	(	int	maxlevel,
		strref	chanfilter,
		uint32	size,
		LogSerializer *	ser
	)

Register a memory buffer log destination

Allocates a fixed-size circular buffer and registers it with the logging system in one step. Records are serialized and written to the buffer; messages longer than the buffer size are dropped, and when the buffer fills, writing wraps back to the beginning. The buffer is freed when logUnregisterDest() retires the returned handle.

Use logmembufData() to reach the buffer contents.

Parameters

maxlevel	Maximum log level to write to the buffer
chanfilter	Channel path pattern, or NULL for every unrestricted channel
size	Buffer size in bytes
ser	Serializer to render records with; ownership transfers, including if this call fails. NULL gets a compact text serializer: short levels, bracketed channels, second-resolution timestamps.

Returns

Destination handle for later unregistration, or NULL on failure

LogDest *dest = logmembufRegister(LOG_Debug, NULL, 8192, NULL);   // 8KB, compact text
 
// or capture structured records for a test to parse
LogDest *jdest = logmembufRegister(LOG_Debug, NULL, 8192, logNdjsonSerializer(NULL));