Android LocalServerSocket

Question

In android, there are two classes LocalServerSocket and LocalSocket. I think they are something like AF_LOCAL in unix socket (I am not sure it is correct or not).

My que

Answer 1

Confirmed that the above works properly. The following examples will not only work together, but will work with the corresponding Android LocalSocket and LocalServerSocket classes:

Client side (Android is server using LocalServerSocket):

#include       /* for printf() and fprintf() */
#include  /* for socket(), connect(), send(), and recv() */
#include      /* struct sockaddr_un */
#include      /* for atoi() and exit() */
#include      /* for memset() */
#include      /* for close() */
#include 
#include 

#define RCVBUFSIZE 2048   /* Size of receive buffer */

void DieWithError(char *errorMessage)  /* Error handling function */
{
    fprintf(stderr, "Error: %s - %s\n", errorMessage, strerror(errno));
    exit(errno);
}

int main(int argc, char *argv[])
{
    int sock;                        /* Socket descriptor */
    struct sockaddr_un echoServAddr; /* Echo server address */
    unsigned char *localSocketName = "MyTestSocket";
    static unsigned char echoString[] = {0x80, 0x00, 0x0e, 0x10, 0x00, 0x9c, 0x40, 0xc9, 0x20, 0x20, 0x20, 0x32, 0x00, 0x00};
    static unsigned int echoStringLen = sizeof(echoString); /* Length of string to echo */
    unsigned char echoBuffer[RCVBUFSIZE]; /* Buffer for echo string */
    int bytesRcvd, totalBytesRcvd;   /* Bytes read in single recv() 
                                    and total bytes read */
    int size;
    int i;

    /* Create a reliable, stream socket using Local Sockets */
    if ((sock = socket(PF_LOCAL, SOCK_STREAM, 0)) < 0)
        DieWithError("socket() failed");

    /* Construct the server address structure */
    memset(&echoServAddr, 0, sizeof(echoServAddr));     /* Zero out structure */
    echoServAddr.sun_family      = AF_LOCAL;            /* Local socket address family */
    /**
     * Tricky and obscure! For a local socket to be in the "Android name space":
     * - The name of the socket must have a 0-byte value as the first character
     * - The linux man page is right in that 0 bytes are NOT treated as a null terminator.
     * - The man page is not clear in its meaning when it states that "the rest of the bytes in
     *        sunpath" are used. "Rest of bytes" is determined by the length passed in for
     *        sockaddr_len and Android sets this per the recommended file-system sockets of
     *        sizeof(sa_family_t) + strlen(sun_path) + 1. This is important when making calls
     *        to bind, connect, etc!
     * We have initialized the struct sockaddr_un to zero already, so all that is needed is to
     * begin the name copy at sun_path[1] and restrict its length to sizeof(echoServAddr.sun_path)-2
     **/
    strncpy(echoServAddr.sun_path + 1, localSocketName, sizeof(echoServAddr.sun_path) - 2); 
    size = sizeof(echoServAddr) - sizeof(echoServAddr.sun_path) + strlen(echoServAddr.sun_path+1) + 1;

    /* Establish the connection to the echo server */
    if (connect(sock, (struct sockaddr *) &echoServAddr, size) < 0)
        DieWithError("connect() failed");

    /* Send the string to the server */
    if (send(sock, echoString, echoStringLen, 0) != echoStringLen)
        DieWithError("send() sent a different number of bytes than expected");

    /* Receive the same string back from the server */
    totalBytesRcvd = 0;
    printf("Sent:     ");
    for (i = 0; i < echoStringLen; i++)
        printf("%02X ", echoString[i]);
    printf("\n");    /* Print a final linefeed */

    printf("Received: ");                /* Setup to print the echoed string */
    if ((bytesRcvd = recv(sock, echoBuffer, RCVBUFSIZE - 1, 0)) <= 0)
        DieWithError("recv() failed or connection closed prematurely");
    for (i = 0; i < bytesRcvd; i++)
        printf("%02X ", echoBuffer[i]);
    printf("\n");    /* Print a final linefeed */

    close(sock);
    exit(0);
}

Server side (Android is client using LocalSocket):

#include       /* for printf() and fprintf() */
#include  /* for socket(), connect(), send(), and recv() */
#include      /* struct sockaddr_un */
#include      /* for atoi() and exit() */
#include      /* for memset() */
#include      /* for close() */
#include 
#include 

#define RCVBUFSIZE 2048   /* Size of receive buffer */

void DieWithError(char *errorMessage)  /* Error handling function */
{
    fprintf(stderr, "Error: %s - %s\n", errorMessage, strerror(errno));
    exit(errno);
}

void HandleLocalClient(int clntSocket)
{
    char echoBuffer[RCVBUFSIZE];        /* Buffer for echo string */
    int recvMsgSize;                    /* Size of received message */

    /* Receive message from client */
    if ((recvMsgSize = recv(clntSocket, echoBuffer, RCVBUFSIZE, 0)) < 0)
        DieWithError("recv() failed");

    /* Send received string and receive again until end of transmission */
    while (recvMsgSize > 0)      /* zero indicates end of transmission */
    {
        /* Echo message back to client */
        if (send(clntSocket, echoBuffer, recvMsgSize, 0) != recvMsgSize)
            DieWithError("send() failed");

        /* See if there is more data to receive */
        if ((recvMsgSize = recv(clntSocket, echoBuffer, RCVBUFSIZE, 0)) < 0)
            DieWithError("recv() failed");
    }

    close(clntSocket);    /* Close client socket */
}

#define MAXPENDING 5    /* Maximum outstanding connection requests */

void DieWithError(char *errorMessage);  /* Error handling function */
void HandleLocalClient(int clntSocket);   /* TCP client handling function */

int main(int argc, char *argv[])
{
    int servSock;                    /* Socket descriptor for server */
    int clntSock;                    /* Socket descriptor for client */
    struct sockaddr_un echoClntAddr; /* Client address */
    unsigned int clntLen;            /* Length of client address data structure */
    struct sockaddr_un echoServAddr; /* Echo server address */
    unsigned char *localSocketName = "MyTestSocket";
    static unsigned int echoStringLen = 14;      /* Length of string to echo */
    unsigned char echoBuffer[RCVBUFSIZE];     /* Buffer for echo string */
    int bytesRcvd, totalBytesRcvd;   /* Bytes read in single recv() 
                                    and total bytes read */
    int size;
    int i;

    /* Create a reliable, stream socket using Local Sockets */
    if ((servSock = socket(PF_LOCAL, SOCK_STREAM, 0)) < 0)
        DieWithError("socket() failed");

    /* Construct the server address structure */
    memset(&echoServAddr, 0, sizeof(echoServAddr));     /* Zero out structure */
    echoServAddr.sun_family      = AF_LOCAL;            /* Local socket address family */
    /**
     * Tricky and obscure! For a local socket to be in the "Android name space":
     * - The name of the socket must have a 0-byte value as the first character
     * - The linux man page is right in that 0 bytes are NOT treated as a null terminator.
     * - The man page is not clear in its meaning when it states that "the rest of the bytes in
     *        sunpath" are used. "Rest of bytes" is determined by the length passed in for
     *        sockaddr_len and Android sets this per the recommended file-system sockets of
     *        sizeof(sa_family_t) + strlen(sun_path) + 1. This is important when making calls
     *        to bind, connect, etc!
     * We have initialized the struct sockaddr_un to zero already, so all that is needed is to
     * begin the name copy at sun_path[1] and restrict its length to sizeof(echoServAddr.sun_path)-2
     **/
    strncpy(echoServAddr.sun_path + 1, localSocketName, sizeof(echoServAddr.sun_path) - 2); 
    size = sizeof(echoServAddr) - sizeof(echoServAddr.sun_path) + strlen(echoServAddr.sun_path+1) + 1;

    /* Bind to the local address */
    if (bind(servSock, (struct sockaddr *) &echoServAddr, size) < 0)
        DieWithError("bind() failed");

    /* Mark the socket so it will listen for incoming connections */
    if (listen(servSock, MAXPENDING) < 0)
        DieWithError("listen() failed");

    for (;;) /* Run forever */
    {
        /* Set the size of the in-out parameter */
        clntLen = sizeof(echoClntAddr);

        /* Wait for a client to connect */
        if ((clntSock = accept(servSock, (struct sockaddr *) &echoClntAddr, &clntLen)) < 0)
            DieWithError("accept() failed");

        /* clntSock is connected to a client! */

        printf("Handling client\n");

        HandleLocalClient(clntSock);
    }
    /* NOT REACHED */
    return 0;
}

Tested with Android 4.0.3 ICS 03/15