From c1bfad9098d94caa4cc2fe64be6b552f4010a0b7 Mon Sep 17 00:00:00 2001
From: Lucas Czech <lucas.czech@h-its.org>
Date: Wed, 23 Mar 2022 11:16:18 +0000
Subject: [PATCH] Add hts_log callback function and hts_log_set_logger()

[DRAFT] Needs documentation in htslib/hts_log.h.

Co-Authored-By: John Marshall <jmarshall@hey.com>
---
 hts.c            | 21 +++++++++++++++++----
 htslib/hts_log.h |  6 ++++++
 test/sam.c       | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 55 insertions(+), 4 deletions(-)

diff --git a/hts.c b/hts.c
index 30c0c6890..9448d7f75 100644
--- a/hts.c
+++ b/hts.c
@@ -4754,19 +4754,32 @@ static char get_severity_tag(enum htsLogLevel severity)
     return '*';
 }
 
+static hts_log_func *hts_logger = NULL;
+static void *hts_logger_data = NULL;
+
+void hts_log_set_logger(hts_log_func *logger, void *data)
+{
+    hts_logger = logger;
+    hts_logger_data = data;
+}
+
 void hts_log(enum htsLogLevel severity, const char *context, const char *format, ...)
 {
     int save_errno = errno;
     if (severity <= hts_verbose) {
         va_list argptr;
 
-        fprintf(stderr, "[%c::%s] ", get_severity_tag(severity), context);
-
         va_start(argptr, format);
-        vfprintf(stderr, format, argptr);
+        if (hts_logger) {
+            hts_logger(hts_logger_data, severity, get_severity_tag(severity), context, format, argptr);
+        }
+        else {
+            fprintf(stderr, "[%c::%s] ", get_severity_tag(severity), context);
+            vfprintf(stderr, format, argptr);
+            fprintf(stderr, "\n");
+        }
         va_end(argptr);
 
-        fprintf(stderr, "\n");
     }
     errno = save_errno;
 }
diff --git a/htslib/hts_log.h b/htslib/hts_log.h
index b2336a4df..b6af29b81 100644
--- a/htslib/hts_log.h
+++ b/htslib/hts_log.h
@@ -29,6 +29,7 @@ SOFTWARE.
 #ifndef HTS_LOG_H
 #define HTS_LOG_H
 
+#include <stdarg.h>
 #include "hts_defs.h"
 
 #ifdef __cplusplus
@@ -89,6 +90,11 @@ HTS_FORMAT(HTS_PRINTF_FMT, 3, 4);
 /*! Logs an event with severity HTS_LOG_TRACE and default context. Parameters: format, ... */
 #define hts_log_trace(...) hts_log(HTS_LOG_TRACE, __func__, __VA_ARGS__)
 
+typedef void hts_log_func(void *data, enum htsLogLevel severity, char severity_tag, const char *context, const char *format, va_list args);
+
+HTSLIB_EXPORT
+void hts_log_set_logger(hts_log_func *logger, void *data);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/test/sam.c b/test/sam.c
index cc5bfe77a..e4ddbf37a 100644
--- a/test/sam.c
+++ b/test/sam.c
@@ -1874,6 +1874,37 @@ static void test_mempolicy(void)
     }
 }
 
+static void my_logger(void *data, enum htsLogLevel severity, char severity_tag, const char *context, const char *format, va_list args)
+{
+    char msg[200];
+    int *nptr = (int *) data;
+    (*nptr)++;
+
+    if (severity != HTS_LOG_ERROR) fail("my_logger saw the wrong message");
+
+    vsprintf(msg, format, args);
+    if (strcmp(msg, "YOU SHOULD NOT SEE THIS MESSAGE") != 0)
+        fail("my_logger message was incorrect: \"%s\"", msg);
+}
+
+static void test_logging(void)
+{
+    int old_level = hts_get_log_level();
+    int n = 0;
+
+    hts_set_log_level(HTS_LOG_WARNING);
+
+    hts_log_set_logger(my_logger, &n);
+    hts_log_error("YOU SHOULD NOT SEE %s", "THIS MESSAGE");
+    if (n != 1) fail("test_logging message one was not redirected");
+
+    hts_log_set_logger(NULL, NULL);
+    hts_log_warning("(expect to see this message)");
+    if (n != 1) fail("test_logging message two was redirected");
+
+    hts_set_log_level(old_level);
+}
+
 static void test_bam_set1_minimal()
 {
     int r;
@@ -2227,6 +2258,7 @@ int main(int argc, char **argv)
     check_big_ref(1);
     test_parse_decimal();
     test_mempolicy();
+    test_logging();
     set_qname();
     for (i = 1; i < argc; i++) faidx1(argv[i]);