一步步DIY: OSM-Web服务器(八) 使用 C FCGI 返回瓦片并登记下载
卫星图片没有相应的mod_tile可以使用，故而需要我们自己来实现。最简单的方法，就是利用 libfcgi-dev 来写一个C的web-service，通过http://...//satile.fcgi?nRow=row&nCol=col&nLevel=lev 来下载，同时，对不在本地缓存内的瓦片，去网上下载。网上的下载程序不在fcgi里实现了，那样比较重量。可以把需要下载的瓦片登记下来，交给后台的下载器去下载。
FCGI的核心是返回PNG图片，也就是用 image/PNG 作为头，后面跟着二进制流。返回PNG看似简单，着实调试了很久，原因就是头部那个该死的换行。
#include <stdio.h>#include <stdlib.h>#include <math.h>#include <stdio.h>#include <string.h>#include <unistd.h>#include <sys/stat.h>#include <fcgi_stdio.h>extern unsigned char bufempty [3531];bool regisit_dbtask(int nLevel,int nCol ,int nRow ){ bool succeeded = false; char buffm[4096]; sprintf(buffm,"/media/sf_tiles/satellite/%d/%d/%d.png",nLevel,nCol,nRow); FILE * fp = fopen(buffm,"rb"); if (fp) { fseek (fp,0,SEEK_END); long nLen = ftell(fp); fseek (fp,0,SEEK_SET); if (nLen<=1024*1024) { unsigned char * pBuf = new unsigned char[nLen]; fread(pBuf,nLen,1,fp); fwrite(pBuf,nLen,1,stdout); delete [] pBuf; } fclose(fp); } else { fwrite(bufempty,3531,1,stdout); FILE * foPut = fopen ("/media/sf_tiles/satellite.txt","a+"); if (foPut ) { fseek(foPut,0,SEEK_END); fprintf(foPut,"%d,%d,%d\n",nLevel,nCol,nRow); fclose(foPut); } } return succeeded;}int main(void){ while (FCGI_Accept() >= 0) { char * rawdata = getenv("QUERY_STRING"); //char * server_name = getenv("SERVER_NAME"); int nLevel=0, nCol=0, nRow = 0; printf("Content-type: image/png\n\n"); fflush(stdout); if (rawdata) { int nLen = strlen(rawdata); char * data = new char [nLen+1]; strcpy (data,rawdata); char * pStrLevel = 0, * pStrCol = 0, * pStrRow = 0; char * tmp = 0; tmp = strstr(data,"nLevel="); if (tmp) pStrLevel = tmp; tmp = strstr(data,"nRow="); if (tmp) pStrRow = tmp; tmp = strstr(data,"nCol="); if (tmp) pStrCol = tmp; if (pStrLevel&& pStrCol && pStrRow ) { for (int i=0;i<nLen;i++) if (data[i]=='?'||data[i]=='&') data[i] = 0; nLevel = atoi(pStrLevel +7); nCol = atoi(pStrCol+5); nRow = atoi(pStrRow +5); delete [] data; } else { printf("<p>Error! At least Missing para nRow, nCol ,nLevel.</p>\r\n"); delete [] data; continue; } } if (nLevel<0 || nLevel>18) { printf("<p>Error nLevel! nLevel must between 0~18.</p>\r\n"); continue; } if (nCol<0||nCol>=(1<<nLevel)) { printf("<p>Error n..Col! n...Col must between 0~%d. </p>\r\n", int((1<<nLevel)-1)); continue; } if (nRow<0||nRow>=(1<<nLevel)) { printf("<p>Error n...Row! n...Row must between 0~%d. </p>\r\n", int((1<<nLevel)-1)); continue; } if (true==regisit_dbtask(nLevel,nCol,nRow)) ; } return 0;}