Overriding native getaddrinfo call with getaddrinfo_android on Androi…

…d. The rationale is to support domain name resolution, which does not work from Musl out of the box due to Android-specific networking architecture. On the other hand, OpenSSH compilation for bionic is too painful. So the compromise is to have Musl-based OpenSSH with getaddrinfo wrapper compiled natively for Android.

defines.h

@@ -409,6 +409,18 @@ struct winsize {
 # define howmany(x,y)	(((x)+((y)-1))/(y))
 #endif
 
+/* Alter the name of getaddrinfo to use Android-specific implementation */
+
+#define getaddrinfo getaddrinfo_android
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netdb.h>
+
+int getaddrinfo_android(
+	const char* node, const char* service,
+	const struct addrinfo* hints, struct addrinfo** res);
+
 /* Paths */
 
 #ifdef __ANDROID__

openbsd-compat/Makefile.in

@@ -89,7 +89,8 @@ COMPAT=	arc4random.o \
 	kludge-fd_set.o \
 	openssl-compat.o \
 	libressl-api-compat.o \
-	xcrypt.o
+	xcrypt.o \
+	getaddrinfo.o
 
 PORTS=	port-aix.o \
 	port-irix.o \

openbsd-compat/getaddrinfo.c

@@ -0,0 +1,187 @@
+// Call an external program /system/bin/getaddrinfo
+// to resolve hostnames on Android. This is ugly, but avoids
+// painful compilation of OpenSSH with Android toolchain.
+#ifdef __ANDROID__
+
+#include <arpa/inet.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <malloc.h>
+#include <netdb.h>
+#include <netinet/in.h>
+#include <netinet/ip.h> 
+#include <unistd.h>
+
+int getaddrinfo_android(
+	const char* node, const char* service,
+	const struct addrinfo* hints, struct addrinfo** res)
+{
+	if (!node)
+	{
+		fprintf(stderr, "getaddrinfo_android: Invalid argument \"node\"\n");
+		return EAI_FAIL;
+	}
+
+	if (!service)
+	{
+		fprintf(stderr, "getaddrinfo_android: Invalid argument \"service\"\n");
+		return EAI_FAIL;
+	}
+
+	if (!res)
+	{
+		fprintf(stderr, "getaddrinfo_android: Invalid argument \"res\"\n");
+		return EAI_FAIL;
+	}
+
+	if (!system(NULL))
+	{
+		fprintf(stderr, "getaddrinfo_android: The command line processor is not available\n");
+		return EAI_FAIL;
+	}
+
+	char filename[] = "/tmp/XXXXXX";
+	int fd = mkstemp(filename);
+	if (fd < 1)
+	{
+		fprintf(stderr, "getaddrinfo_android: Could not create a temporary file %s\n", filename);
+		return EAI_FAIL;
+	}
+	unlink(filename);
+
+	int command_printed_size = snprintf(NULL, 0,
+		"%s "  // resolv
+		"%s "  // node
+		">%s", // filename
+		"/system/bin/nslookup",
+		node, filename);
+	if (command_printed_size < 0)
+	{
+		fprintf(stderr, "getaddrinfo_android: Could not encode the command\n");
+		return EAI_FAIL;
+	}
+	char* command = malloc(command_printed_size + 1);
+	sprintf(command,
+		"%s "  // nslookup
+		"%s "  // node
+		">%s", // filename
+		"/system/bin/nslookup",
+		node, filename);
+
+#if 0
+	printf("command = %s\n", command);
+#endif
+
+	// Call the command line resolver utility.
+	int err = system(command);
+	if (err)
+	{
+		fprintf(stderr, "getaddrinfo_android: The resolver command line utility retuned non-zero error code %d\n", err);
+		return EAI_FAIL;
+	}
+	free(command);
+
+	FILE* fp = fopen(filename, "r");
+	if (!fp)
+	{
+		fprintf(stderr, "getaddrinfo_android: Could not read the temporary file %s\n", filename);
+		return EAI_FAIL;
+	}
+
+	// Read the response temporary file to get the result
+	*res = malloc(1);
+	int nres = 0;
+	char* line = NULL;
+	size_t len = 0;
+	ssize_t read;
+	char* name = NULL;
+	char* address = NULL;
+	while ((read = getline(&line, &len, fp)) != -1)
+	{
+		if (strncmp(line, "Name:", strlen("Name:")) == 0)
+		{
+			line[read - 1] = '\0';
+			char* p = line + strlen("Name:");
+			while ((*p == ' ') || (*p == '\t')) p++;
+			if (!name) free(name);
+			name = strdup(p);
+		}
+		else if (strncmp(line, "Address:", strlen("Address:")) == 0)
+		{
+			line[read - 1] = '\0';
+			char* p = line + strlen("Address:");
+			while ((*p == ' ') || (*p == '\t')) p++;
+			if (!address) free(address);
+			address = strdup(p);
+		}
+
+		if (!(name && address))
+			continue;
+
+		nres++;
+		*res = realloc(*res, nres * sizeof((*res)[0]));
+		struct addrinfo* r = &(*res)[nres - 1];
+		memset(r, 0, sizeof((*res)[0]));
+
+		if (nres > 1)
+			(*res)[nres - 2].ai_next = r;
+
+		r->ai_socktype = SOCK_STREAM;
+		r->ai_flags |= AI_CANONNAME;
+
+		r->ai_canonname = name;
+		name = NULL;
+
+		char buffer[sizeof(struct in6_addr)];
+		if (inet_pton(AF_INET, address, buffer) == 1)
+		{
+			r->ai_family = AF_INET;
+			r->ai_addrlen = sizeof(struct sockaddr_in);
+			struct sockaddr_in* addr = malloc(sizeof(struct sockaddr_in));
+			memset(addr, 0, sizeof(struct sockaddr_in));
+			addr->sin_family = AF_INET;
+			addr->sin_port = htons(atoi(service));
+			memcpy(&addr->sin_addr, buffer, sizeof(struct in_addr));
+			r->ai_addr = addr;
+		}
+		else if (inet_pton(AF_INET6, address, buffer) == 1)
+		{
+			r->ai_family = AF_INET6;
+			r->ai_addrlen = sizeof(struct sockaddr_in6);
+			struct sockaddr_in6* addr = malloc(sizeof(struct sockaddr_in6));
+			memset(addr, 0, sizeof(struct sockaddr_in6));
+			addr->sin6_family = AF_INET6;
+			addr->sin6_port = htons(atoi(service));
+			memcpy(&addr->sin6_addr, buffer, sizeof(struct in6_addr));
+			r->ai_addr = addr;
+		}
+		else
+		{
+			fprintf(stderr, "getaddrinfo_android: Invalid address value \"%s\"\n", address);
+
+			free(address);
+			free(*res);
+			return EAI_FAIL;
+		}
+
+		free(address);
+		address = NULL;
+	}
+
+	fclose(fp);
+	close(fd);
+
+	if (!nres)
+	{
+		free(*res);
+		*res = NULL;
+	}
+
+	return 0;
+}
+
+#endif // __ANDROID__
+