logcat: Create liblogcat

Try to leverage as much of logcat as-is and produce a viable
library API that others can use for their own logcat execution.

Added a test to check ANDROID_PRINTF_LOG environment variable.

Test: gTest logcat-unit-tests
Bug: 35326290
Change-Id: I30de692ea9d83e6fd6e5d9e7cf93d31401a88a40

logcat/Android.mk

@@ -1,20 +1,32 @@
 # Copyright 2006-2014 The Android Open Source Project
 
-LOCAL_PATH:= $(call my-dir)
+LOCAL_PATH := $(call my-dir)
+
+logcatLibs := liblog libbase libcutils libpcrecpp
+
 include $(CLEAR_VARS)
 
-LOCAL_SRC_FILES:= logcat.cpp event.logtags
-
-LOCAL_SHARED_LIBRARIES := liblog libbase libcutils libpcrecpp
-
 LOCAL_MODULE := logcat
-
+LOCAL_SRC_FILES := logcat_main.cpp event.logtags
+LOCAL_SHARED_LIBRARIES := liblogcat $(logcatLibs)
+LOCAL_C_INCLUDES := $(LOCAL_PATH)/include
 LOCAL_CFLAGS := -Werror
 
 include $(BUILD_EXECUTABLE)
 
 include $(CLEAR_VARS)
 
+LOCAL_MODULE := liblogcat
+LOCAL_SRC_FILES := logcat.cpp
+LOCAL_SHARED_LIBRARIES := $(logcatLibs)
+LOCAL_C_INCLUDES := $(LOCAL_PATH)/include
+LOCAL_EXPORT_C_INCLUDES_DIR := $(LOCAL_PATH)/include
+LOCAL_CFLAGS := -Werror
+
+include $(BUILD_SHARED_LIBRARY)
+
+include $(CLEAR_VARS)
+
 LOCAL_MODULE := logpersist.start
 LOCAL_MODULE_TAGS := debug
 LOCAL_MODULE_CLASS := EXECUTABLES

logcat/include/log/logcat.h

@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2005-2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _LIBS_LOGCAT_H /* header boilerplate */
+#define _LIBS_LOGCAT_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef __ANDROID_USE_LIBLOG_LOGCAT_INTERFACE
+#ifndef __ANDROID_API__
+#define __ANDROID_USE_LIBLOG_LOGCAT_INTERFACE 1
+#elif __ANDROID_API__ > 24 /* > Nougat */
+#define __ANDROID_USE_LIBLOG_LOGCAT_INTERFACE 1
+#else
+#define __ANDROID_USE_LIBLOG_LOGCAT_INTERFACE 0
+#endif
+#endif
+
+#if __ANDROID_USE_LIBLOG_LOGCAT_INTERFACE
+
+/* For managing an in-process logcat function, rather than forking/execing
+ *
+ * It also serves as the basis for the logcat command.
+ *
+ * The following C API allows a logcat instance to be created, run
+ * to completion, and then release all the associated resources.
+ */
+
+/*
+ * The opaque context
+ */
+#ifndef __android_logcat_context_defined /* typedef boilerplate */
+#define __android_logcat_context_defined
+typedef struct android_logcat_context_internal* android_logcat_context;
+#endif
+
+/* Creates a context associated with this logcat instance
+ *
+ * Returns a pointer to the context, or a NULL on error.
+ */
+android_logcat_context create_android_logcat();
+
+/* Collects and outputs the logcat data to output and error file descriptors
+ *
+ * Will block, performed in-thread and in-process
+ *
+ * The output file descriptor variable, if greater than or equal to 0, is
+ * where the output (ie: stdout) will be sent. The file descriptor is closed
+ * on android_logcat_destroy which terminates the instance, or when an -f flag
+ * (output redirect to a file) is present in the command.  The error file
+ * descriptor variable, if greater than or equal to 0, is where the error
+ * stream (ie: stderr) will be sent, also closed on android_logcat_destroy.
+ * The error file descriptor can be set to equal to the output file descriptor,
+ * which will mix output and error stream content, and will defer closure of
+ * the file descriptor on -f flag redirection.  Negative values for the file
+ * descriptors will use stdout and stderr FILE references respectively
+ * internally, and will not close the references as noted above.
+ *
+ * Return value is 0 for success, non-zero for errors.
+ */
+int android_logcat_run_command(android_logcat_context ctx, int output, int error,
+                               int argc, char* const* argv, char* const* envp);
+
+/* Finished with context
+ *
+ * Free up all associated resources.
+ *
+ * Return value is the result of the android_logcat_run_command, or
+ * non-zero for any errors.
+ */
+int android_logcat_destroy(android_logcat_context* ctx);
+
+#endif /* __ANDROID_USE_LIBLOG_LOGCAT_INTERFACE */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _LIBS_LOGCAT_H */

logcat/logcat_main.cpp

@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <signal.h>
+#include <stdlib.h>
+
+#include <log/logcat.h>
+
+int main(int argc, char** argv, char** envp) {
+    android_logcat_context ctx = create_android_logcat();
+    if (!ctx) return -1;
+    signal(SIGPIPE, exit);
+    int retval = android_logcat_run_command(ctx, -1, -1, argc, argv, envp);
+    int ret = android_logcat_destroy(&ctx);
+    if (!ret) ret = retval;
+    return ret;
+}

logcat/tests/logcat_test.cpp

@@ -278,7 +278,7 @@ static void do_tail(int num) {
         char buffer[BIG_BUFFER];
 
         snprintf(buffer, sizeof(buffer),
-                 "logcat -v long -b all -t %d 2>/dev/null", num);
+                 "ANDROID_PRINTF_LOG=long logcat -b all -t %d 2>/dev/null", num);
 
         FILE* fp;
         ASSERT_TRUE(NULL != (fp = popen(buffer, "r")));