Error writing and reading a structure from PIPE - unix

Question

I have a client server program where client writes a command on PIPE for server. While reading the command from Server it reads only first char of command and throws error. Can anyone help me with this?
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <string.h>
#include <sys/wait.h>
#include <mqueue.h>
#include <sys/stat.h>
#include "Functions.h"
#define MSGBUFFER_SIZE 50000
pid_t serverPid;
pid_t clientPid;
typedef struct msgbuf {
int messageLength;
int messageType;
char messageText[MSGBUFFER_SIZE];
} Message_buf;
int writePIPE(int fd, Message_buf *inputMessage){
printf("\n In write pipe message length :%d",inputMessage->messageLength);
printf("\n In write pipe message Data :%s",inputMessage->messageText);
ssize_t n=write(fd,inputMessage,inputMessage->messageLength);
printf("\n Size :%d", n);
return n;
}
ssize_t readPIPE(int fd, Message_buf *outputMessage)
{
ssize_t len;
ssize_t n;
if((n=read(fd,outputMessage,sizeof(outputMessage)))==0)
{
printf("\n Error");
return 0;
}
if((len=outputMessage->messageLength)>0)
{
printf("\n Length ---->:%d",len);
if((n=read(fd,outputMessage->messageText,strlen(outputMessage->messageText)))!=len)
printf("\n ERRRRROR expected %d got %d",len,n);
}
//printf("\n In Read PIPE: %s",outputMessage->messageText);
return len;
}
void Server(int readfd,int writefd)
{
Message_buf server_MessageBuf;
ssize_t length;
if((length=readPIPE(readfd,&server_MessageBuf))==0)
{
printf("\n End of file while reading pathname");
}
//server_MessageBuf.messageText[length]='\0';
printf("\n LENGTH :%d",server_MessageBuf.messageLength);
printf("\n Printing in server: %s\n",server_MessageBuf.messageText);
}
void Client(int readfd,int writefd)
{
char inputFileName[MAX_SIZE];
char inputOperation[MAX_SIZE];
char *cCommandInput = NULL;
char *fileOperation = NULL;
char *operation = (char *) malloc(MAX_SIZE);
int commandValidateStatus = 0;
int commandInterpretationStatus=0;
Message_buf client_MessageBuf;
for(;;)
{
while(1)
{
cCommandInput = acceptInput();
fileOperation = (char *) malloc(sizeof(cCommandInput));
strcpy(fileOperation,cCommandInput);
/**Function call to determine operation read/delete/exit/invalid choice and filename*****/
commandInterpretationStatus = interpretCommand(cCommandInput,
inputOperation, inputFileName);
operation = inputOperation;
/**Function call to validate the input command******/
commandValidateStatus = validateCommand(
commandInterpretationStatus, inputOperation, inputFileName);
if(commandValidateStatus==-1)
{
printf("\n Invalid Operation");
}
/*Exit command entered***/
if (commandValidateStatus == 1)
{
/*Code to clear resources */
kill(serverPid,SIGKILL);
kill(clientPid,SIGKILL);
exit(0);
}
/***Read or Delete****/
if (commandValidateStatus == 2 || commandValidateStatus == 3)
{
printf("\n Read or Delete\n");
strcpy(client_MessageBuf.messageText,fileOperation);
client_MessageBuf.messageLength=strlen(fileOperation);
client_MessageBuf.messageType=1;
if((writePIPE(writefd,&client_MessageBuf))<0)
{
printf("\n Error writing on client side ");
}
//read(readfd,*client_MessageBuf,sizeof(client_MessageBuf));
//printf("\n Reding server responsed");
//printf("%s",client_MessageBuf.messageText);
}
}
}
}
int main()
{
int pipe1[2],pipe2[2];
pipe(pipe1);
pipe(pipe2);
pid_t pid;
pid=fork();
serverPid=pid;
if(pid==0)
{
/*Call Server*/
close(pipe1[1]);
close(pipe2[0]);
Server(pipe1[0], pipe2[1]);
}
else
{
close(pipe1[0]);
close(pipe2[1]);
Client(pipe2[0],pipe1[1]);
}
return 0;
}

Answer 1

It looks like the code writes and reads struct msgbuf incorrectly:
typedef struct msgbuf {
int messageLength;
int messageType;
char messageText[MSGBUFFER_SIZE];
} Message_buf;
// ...
strcpy(client_MessageBuf.messageText,fileOperation);
client_MessageBuf.messageLength=strlen(fileOperation);
client_MessageBuf.messageType=1;
if((writePIPE(writefd,&client_MessageBuf))<0)
// ....
int writePIPE(int fd, Message_buf *inputMessage){
printf("\n In write pipe message length :%d",inputMessage->messageLength);
printf("\n In write pipe message Data :%s",inputMessage->messageText);
ssize_t n=write(fd,inputMessage,inputMessage->messageLength);
printf("\n Size :%d", n);
return n;
}
The above pieces that write struct msgbuf only write the first messageLength bytes of the structure which doesn't include the length of messageLength and messageType members, i.e. it truncates the object.
When reading:
ssize_t readPIPE(int fd, Message_buf *outputMessage)
{
// ...
if((n=read(fd,outputMessage,sizeof(outputMessage)))==0)
It reads only sizeof(outputMessage) bytes, which is the size of the pointer, not the object. Even if you fix it by changing it to sizeof(*outputMessage) that won't do enough, since that would expect to read the complete object whereas the writing piece truncates the object.
A good start to fix it would be to split the message into two parts: header and payload. The header is a structure of a fixed size, e.g.:
typedef struct {
int messageType;
int payloadLength;
} MessageHeader;
The payload is a variable-length part following the header. This way it would first write the entire header object into the pipe followed by payloadLength bytes of payload. When reading it would first read again the entire header and then read exactly payloadLength bytes.
Also note, that read() and write() calls may read or write less then asked, so that case needs to be explicitly handled by keeping reading or writing until the exact number of bytes has been processed.