Redis module development environment

This document outlines the set up of a development environment for Redis Modules.

Prerequisites

1. A Linux server (e.g. Ubuntu Gnome 16.10)
2. Packages: sudo apt install build-essential git
3. Redis unstable: git clone git@github.com:antirez/redis.git; cd redis; make

An example module

1. Create the project's directory: mkdir example; cd example

2. Get the API's header file: cp ../redis/src/redismodule.h .

3. Edit example.c:

   #include "redismodule.h"
   
   int Echo(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
   {
       if (argc != 2)
           return RedisModule_WrongArity(ctx);
   
       return RedisModule_ReplyWithString(ctx, argv[1]);
   }
   
   int RedisModule_OnLoad(RedisModuleCtx *ctx)
   {
       if (RedisModule_Init(ctx, "example", 1, REDISMODULE_APIVER_1) == REDISMODULE_ERR)
           return REDISMODULE_ERR;
   
       if (RedisModule_CreateCommand(ctx, "example.echo", Echo, "readonly", 0, 0, 0) == REDISMODULE_ERR)
           return REDISMODULE_ERR;
   
       return REDISMODULE_OK;
   }

4. Compile it: gcc -fPIC -std=gnu99 -c -o example.o example.c

5. Link it: ld -o example.so example.o -shared -Bsymbolic -lc

6. Load it: ../redis/src/redis-server --loadmodule ./example.so

7. Test it: ../redis/src/redis-cli example.echo tango

Adding a makefile

1. Edit Makefile:

   SHOBJ_CFLAGS ?= -fno-common -g -ggdb
   SHOBJ_LDFLAGS ?= -shared -Bsymbolic
   CFLAGS = -Wall -g -fPIC -lc -lm -Og -std=gnu99  
   CC=gcc
   
   all: example.so
   
   example.so: example.o
       $(LD) -o $@ example.o $(SHOBJ_LDFLAGS) $(LIBS) -lc 
   
   clean:
       rm -rf *.xo *.so *.o

Redis Modules SDK

Tools, utilities and scripts to help you write Redis modules!

git clone git@github.com:RedisLabs/RedisModulesSDK.git

Includes:

• A ready-to-use example module
• The API's documentation
• String, memory management and testing utilties
• Vector, heap and priority queue implementations
• More... (and accepting pull requests)

Testing the module

The a simple approach is to have the module expose an entry point for running basic sanity tests:

1. Register a test command for the module by adding this to RedisModule_OnLoad:

   if (RedisModule_CreateCommand(ctx, "example.test", Test, "readonly", 0, 0, 0) == REDISMODULE_ERR)
       return REDISMODULE_ERR;
   

2. Implement the Test function:

   int Test(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
       REDISMODULE_NOT_USED(argv);
       REDISMODULE_NOT_USED(argc);
       RedisModule_AutoMemory(ctx);
   
       RedisModuleString *str = RedisModule_CreateString(ctx, "test", 4);
       RedisModuleCallReply *reply = RedisModule_Call(ctx, "example.echo", "s", str);
       
       if (REDISMODULE_REPLY_STRING != RedisModule_CallReplyType(reply)) {
           RedisModule_ReplyWithError(ctx, "Unexpected reply type");
           return REDISMODULE_ERR;
       }
   
       RedisModuleString *rstr = RedisModule_CreateStringFromCallReply(reply);
       if (RedisModule_StringCompare(str, rstr) != 0) {
           RedisModule_ReplyWithError(ctx, "Unexpected reply");
           return REDISMODULE_ERR;
       }
   
       RedisModule_ReplyWithSimpleString(ctx, "OK");
       return REDISMODULE_OK;
   
   }

Some notes:

• Refer to redis/src/modules/testmodule.c and the SDK for a more implementation examples.
• Test execution requires a running server, the module loaded and a client -> extra effort needed to automate unit tests.
• Can be extended/augmented/replaced with other testing frameworks. For example, RediSearch uses pytest and a disposable Redis class.

Setting up Visual Studio Code

1. Get Visual Studio Code

2. You'll also need clang: sudo apt install clang

3. Run it and open the project's folder

4. Install extensions (Ctrl+Shift+X):

   1. C/++ (ms-vscode.cpptools)
   2. C/C++ Clang (mitaki28.vscode-clang)

5. Configure the launcher's run task:

   1. Hit F5
   2. Select "C++ (GDB/LLDB)"
   3. Edit launch.json to:

   {
       "version": "0.2.0",
       "configurations": [
           {
               "name": "Launch Redis with module",
               "type": "cppdbg",
               "request": "launch",
               "program": "${workspaceRoot}/../redis/src/redis-server",
               "args": ["--loadmodule ${workspaceRoot}/example.so"],
               "stopAtEntry": false,
               "cwd": "${workspaceRoot}",
               "environment": [],
               "internalConsoleOptions": "openOnSessionStart",
               "linux": {
                   "MIMode": "gdb"
               }
           }
       ]
   }

6. Configure the build task:

   1. Ctrl+Shift+B -> Configure Task Runner
   2. Select "Others"
   3. Edit tasks.json to:

   {
       "version": "0.1.0",
       "command": "make",
       "isShellCommand": true,
       "tasks": [
           {
               "taskName": "all",
               "isBuildCommand": true
           }
       ]
   }