MXS-1347: Expose unified log file as a module command

The qlafilter exposes the unified log file as a module command that
outputs an array of JSON strings, one for each line in the file. The
command takes two optional parameters, the start and end lines for the log
file.

Further improvements could be done to allow reading of session specific
log files.

Some sort of an authorization scheme for the REST API should be
implemented to limit the possibility of exposing unwanted parts of the
REST API.

server/modules/filter/qlafilter/qlafilter.cc

@@ -31,6 +31,8 @@
 #include <stdio.h>
 #include <string.h>
 #include <sys/time.h>
+#include <fstream>
+
 #include <maxscale/alloc.h>
 #include <maxscale/atomic.h>
 #include <maxscale/filter.h>
@@ -40,6 +42,8 @@
 #include <maxscale/pcre2.h>
 #include <maxscale/service.h>
 #include <maxscale/utils.h>
+#include <maxscale/modulecmd.h>
+#include <maxscale/json_api.h>
 
 /* Date string buffer size */
 #define QLA_DATE_BUFFER_SIZE 20
@@ -96,6 +100,7 @@ typedef struct
     uint32_t log_file_data_flags; /* What data is saved to the files */
     FILE *unified_fp; /* Unified log file. The pointer needs to be shared here
                        * to avoid garbled printing. */
+    char *unified_filename; /* Filename of the unified log file */
     bool flush_writes; /* Flush log file after every write? */
     bool append;    /* Open files in append-mode? */
 
@@ -120,6 +125,7 @@ typedef struct
 static FILE* open_log_file(uint32_t, QLA_INSTANCE *, const char *);
 static int write_log_entry(uint32_t, FILE*, QLA_INSTANCE*, QLA_SESSION*, const char*,
                            const char*, size_t);
+static bool cb_log(const MODULECMD_ARG *argv, json_t** output);
 
 static const MXS_ENUM_VALUE option_values[] =
 {
@@ -166,6 +172,26 @@ MXS_BEGIN_DECLS
  */
 MXS_MODULE* MXS_CREATE_MODULE()
 {
+    modulecmd_arg_type_t args[] =
+    {
+        {
+            MODULECMD_ARG_FILTER | MODULECMD_ARG_NAME_MATCHES_DOMAIN,
+            "Filter to read logs from"
+        },
+        {
+            MODULECMD_ARG_STRING | MODULECMD_ARG_OPTIONAL,
+            "Start reading from this line"
+        },
+        {
+            MODULECMD_ARG_STRING | MODULECMD_ARG_OPTIONAL,
+            "Stop reading at this line (exclusive)"
+        }
+    };
+
+    modulecmd_register_command(MXS_MODULE_NAME, "log",
+                               MODULECMD_TYPE_PASSIVE, cb_log, 3, args,
+                               "Show unified log file as a JSON array");
+
     static MXS_FILTER_OBJECT MyObject =
     {
         createInstance,
@@ -278,6 +304,7 @@ createInstance(const char *name, char **options, MXS_CONFIG_PARAMETER *params)
         my_instance->sessions = 0;
         my_instance->ovec_size = 0;
         my_instance->unified_fp = NULL;
+        my_instance->unified_filename = NULL;
         my_instance->write_warning_given = false;
 
         my_instance->source = config_copy_string(params, PARAM_SOURCE);
@@ -321,11 +348,15 @@ createInstance(const char *name, char **options, MXS_CONFIG_PARAMETER *params)
 
                 if (my_instance->unified_fp == NULL)
                 {
+                    MXS_FREE(filename);
                     MXS_ERROR("Opening output file for qla-filter failed due to %d, %s",
                               errno, mxs_strerror(errno));
                     error = true;
                 }
-                MXS_FREE(filename);
+                else
+                {
+                    my_instance->unified_filename = filename;
+                }
             }
             else
             {
@@ -903,3 +934,55 @@ static int write_log_entry(uint32_t data_flags, FILE *logfile, QLA_INSTANCE *ins
         return rval;
     }
 }
+
+static bool cb_log(const MODULECMD_ARG *argv, json_t** output)
+{
+    ss_dassert(argv->argc > 0);
+    ss_dassert(argv->argv[0].type.type == MODULECMD_ARG_FILTER);
+
+    MXS_FILTER_DEF* filter = argv[0].argv->value.filter;
+    QLA_INSTANCE* instance = reinterpret_cast<QLA_INSTANCE*>(filter_def_get_instance(filter));
+    bool rval = false;
+
+    if (instance->log_mode_flags & CONFIG_FILE_UNIFIED)
+    {
+        ss_dassert(instance->unified_fp && instance->unified_filename);
+        std::ifstream file(instance->unified_filename);
+
+        if (file)
+        {
+            json_t* arr = json_array();
+            // TODO: Add integer type to modulecmd
+            int start = argv->argc > 1 ? atoi(argv->argv[1].value.string) : 0;
+            int end = argv->argc > 2 ? atoi(argv->argv[2].value.string) : 0;
+            int current = 0;
+
+            /** Skip lines we don't want */
+            for (std::string line; current < start && std::getline(file, line); current++)
+            {
+                ;
+            }
+
+            /** Read lines until either EOF or line count is reached */
+            for (std::string line; std::getline(file, line) && (current < end || end == 0); current++)
+            {
+                json_array_append_new(arr, json_string(line.c_str()));
+            }
+
+            *output = arr;
+            rval = true;
+        }
+        else
+        {
+            *output = mxs_json_error("Failed to open file '%s'",
+                                     instance->unified_filename);
+        }
+    }
+    else
+    {
+        *output = mxs_json_error("Filter '%s' does not have unified log file enabled",
+                                 filter_def_get_name(filter));
+    }
+
+    return rval;
+}