LibC: Add setenv().

If I'm understanding the standard C library correctly, setenv() copies while
putenv() does not. That's really confusing and putenv() basically sucks.
To know which environment variables to free on replacement and which ones to
leave alone, we keep track of the ones malloced by setenv in a side table.

This patch also moves Shell to using setenv() instead of putenv().

Fixes #29.

2 files changed, 25 insertions, 0 deletions

diff --git a/LibC/stdlib.cpp b/LibC/stdlib.cpp
index cabcda573d..74d7d07939 100644
--- a/LibC/stdlib.cpp
+++ b/LibC/stdlib.cpp
@@ -46,6 +46,16 @@ void abort()
     raise(SIGABRT);
 }
 
+static HashTable<char*> s_malloced_environment_variables;
+
+static void free_environment_variable_if_needed(const char* var)
+{
+    if (!s_malloced_environment_variables.contains((char*)var))
+        return;
+    free((void*)var);
+    s_malloced_environment_variables.remove((char*)var);
+}
+
 char* getenv(const char* name)
 {
     size_t vl = strlen(name);
@@ -89,9 +99,22 @@ int unsetenv(const char* name)
     // Shuffle the existing array down by one.
     memmove(&environ[skip], &environ[skip+1], ((environ_size-1)-skip) * sizeof(environ[0]));
     environ[environ_size-1] = nullptr;
+
+    free_environment_variable_if_needed(name);
     return 0;
 }
 
+int setenv(const char* name, const char* value, int overwrite)
+{
+    if (!overwrite && !getenv(name))
+        return 0;
+    auto length = strlen(name) + strlen(value) + 2;
+    auto* var = (char*)malloc(length);
+    snprintf(var, length, "%s=%s", name, value);
+    s_malloced_environment_variables.set(var);
+    return putenv(var);
+}
+
 int putenv(char* new_var)
 {
     char* new_eq = strchr(new_var, '=');
@@ -111,6 +134,7 @@ int putenv(char* new_var)
             continue; // can't match
 
         if (strncmp(new_var, old_var, new_var_len) == 0) {
+            free_environment_variable_if_needed(old_var);
             environ[environ_size] = new_var;
             return 0;
         }
diff --git a/LibC/stdlib.h b/LibC/stdlib.h
index 946a1d8274..a310ee5e11 100644
--- a/LibC/stdlib.h
+++ b/LibC/stdlib.h
@@ -18,6 +18,7 @@ void* realloc(void* ptr, size_t);
 char* getenv(const char* name);
 int putenv(char*);
 int unsetenv(const char*);
+int setenv(const char* name, const char* value, int overwrite);
 int atoi(const char*);
 long atol(const char*);
 long long atoll(const char*);