diff --git a/lnm/include/lnm/common.h b/lnm/include/lnm/common.h
index 381b4c9..4dc789d 100644
--- a/lnm/include/lnm/common.h
+++ b/lnm/include/lnm/common.h
@@ -17,6 +17,9 @@
     }                                                                          \
   }
 
+#define LNM_MIN(x, y) ((x) < (y) ? (x) : (y))
+#define LNM_MAX(x, y) ((x) > (y) ? (x) : (y))
+
 typedef enum {
   lnm_err_ok = 0,
   lnm_err_failed_alloc,
@@ -26,4 +29,12 @@ typedef enum {
   lnm_err_bad_regex
 } lnm_err;
 
+typedef struct lnm_loop lnm_http_loop;
+
+typedef struct lnm_loop_conn lnm_http_conn;
+
+typedef struct lnm_http_step lnm_http_step;
+
+typedef struct lnm_http_route lnm_http_route;
+
 #endif
diff --git a/lnm/include/lnm/http/loop.h b/lnm/include/lnm/http/loop.h
index de0edcd..12ff602 100644
--- a/lnm/include/lnm/http/loop.h
+++ b/lnm/include/lnm/http/loop.h
@@ -7,14 +7,6 @@
 #include "lnm/http/req.h"
 #include "lnm/http/res.h"
 
-typedef struct lnm_loop lnm_http_loop;
-
-typedef struct lnm_loop_conn lnm_http_conn;
-
-typedef struct lnm_http_step lnm_http_step;
-
-typedef struct lnm_http_route lnm_http_route;
-
 typedef enum lnm_http_step_err {
   lnm_http_step_err_done = 0,
   lnm_http_step_err_io_needed,
diff --git a/lnm/include/lnm/http/res.h b/lnm/include/lnm/http/res.h
index 18ae914..8ea7636 100644
--- a/lnm/include/lnm/http/res.h
+++ b/lnm/include/lnm/http/res.h
@@ -2,9 +2,17 @@
 #define LNM_HTTP_RES
 
 #include <stdbool.h>
+#include <stdio.h>
 
+#include "lnm/common.h"
 #include "lnm/http/consts.h"
 
+typedef lnm_err (*data_fn)(size_t *written, char *buf, lnm_http_conn *conn,
+                           size_t offset, size_t len);
+
+/**
+ * Linked list elements used to store the response headers
+ */
 typedef struct lnm_http_res_header {
   struct {
     char *s;
@@ -19,12 +27,85 @@ typedef struct lnm_http_res_header {
   struct lnm_http_res_header *next;
 } lnm_http_res_header;
 
+typedef enum lnm_http_res_body_type {
+  lnm_http_res_body_type_file = 0,
+  lnm_http_res_body_type_buf,
+  lnm_http_res_body_type_fn,
+} lnm_http_res_body_type;
+
 typedef struct lnm_http_res {
   lnm_http_status status;
   struct {
     lnm_http_res_header *head;
     lnm_http_res_header *current;
   } headers;
+  struct {
+    struct {
+      char *buf;
+      FILE *f;
+      data_fn fn;
+    } data;
+    size_t len;
+    bool owned;
+    lnm_http_res_body_type type;
+  } body;
+  // General-purpose; meaning depends on the current state
+  size_t written;
 } lnm_http_res;
 
+/**
+ * Add a new header of a known type to the response
+ *
+ * @param type type of header
+ * @param value null-terminated string containing the value of the header
+ * @param value_owned whether to take ownership of the value pointer; if false,
+ * free'ing the buffer is the caller's responsibility
+ */
+lnm_err lnm_http_res_add_header(lnm_http_res *res, lnm_http_header type,
+                                char *value, bool value_owned);
+
+/**
+ * Add a new header of a known type to the response with a given value length.
+ *
+ * @param type type of header
+ * @param value string of length `value_len` containing the value of the header
+ * @param value_len length of value
+ * @param value_owned whether to take ownership of the value pointer; if false,
+ * free'ing the buffer is the caller's responsibility
+ */
+lnm_err lnm_http_res_add_header_len(lnm_http_res *res, lnm_http_header type,
+                                    char *value, size_t value_len,
+                                    bool value_owned);
+
+/**
+ * Set the request body to the given file pointer.
+ *
+ * @param res response to modify
+ * @param f file pointer to use as data
+ * @param len expected length of the file
+ * @param owned whether to take ownership of the file pointer
+ */
+void lnm_http_res_body_set_file(lnm_http_res *res, FILE *f, size_t len,
+                                bool owned);
+
+/**
+ * Set the request body to the given buffer.
+ *
+ * @param res response to modify
+ * @param buf buffer to use as data
+ * @param len length of the buffer
+ * @param owned whether to take ownership of the file pointer
+ */
+void lnm_http_res_body_set_buf(lnm_http_res *res, char *buf, size_t len,
+                               bool owned);
+
+/**
+ * Set the request body to be read from the given data function.
+ *
+ * @param res response to modify
+ * @param fn data reader function
+ * @param len expected length of the response
+ */
+void lnm_http_res_body_set_fn(lnm_http_res *res, data_fn fn, size_t len);
+
 #endif
diff --git a/lnm/src/http/lnm_http_loop_process.c b/lnm/src/http/lnm_http_loop_process.c
index 5fa4f21..c8aed94 100644
--- a/lnm/src/http/lnm_http_loop_process.c
+++ b/lnm/src/http/lnm_http_loop_process.c
@@ -1,4 +1,5 @@
 #include <stdbool.h>
+#include <stdio.h>
 #include <string.h>
 
 #include "lnm/http/consts.h"
@@ -116,25 +117,139 @@ void lnm_http_loop_process_steps(lnm_http_conn *conn) {
       ctx->state = lnm_http_loop_state_first_res;
       break;
     }
-  } while ((step != ctx->cur_step) && (ctx->cur_step != NULL));
+  }
+  // Loop until we either:
+  // - reach the end of the chain of steps, indicated by NULL
+  // - have a step that's waiting for I/O
+  while ((ctx->cur_step != NULL) && (step != ctx->cur_step));
 
   if (ctx->cur_step == NULL) {
     ctx->state = lnm_http_loop_state_write_headers;
   }
 }
 
+// This function is intentionally written inefficiently for now, as it will most
+// likely only have to run once for each response
+void lnm_http_loop_process_write_status_line(lnm_http_conn *conn) {
+  lnm_http_loop_ctx *ctx = conn->ctx;
+  lnm_http_res *res = &ctx->res;
+
+  const char *response_type_name =
+      lnm_http_status_names[res->status / 100 - 1][res->status % 100];
+
+  // First we calculate the size of the start of the header
+  size_t buf_size =
+      snprintf(NULL, 0, "HTTP/1.1 %i %s\n", res->status, response_type_name);
+  char buf[buf_size + 1];
+  sprintf(buf, "HTTP/1.1 %i %s\n", res->status, response_type_name);
+
+  size_t to_write =
+      LNM_MIN(buf_size - res->written, LNM_LOOP_BUF_SIZE - conn->w.size);
+  memcpy(&conn->w.buf[conn->w.size], &buf[res->written], to_write);
+
+  conn->w.size += to_write;
+  res->written += to_write;
+
+  if (res->written == buf_size) {
+    res->written = 0;
+    ctx->state = lnm_http_loop_state_write_headers;
+  }
+}
+
+void lnm_http_loop_process_write_headers(lnm_http_conn *conn) {
+  lnm_http_loop_ctx *ctx = conn->ctx;
+  lnm_http_res *res = &ctx->res;
+
+  lnm_http_res_header *header = res->headers.current;
+
+  // Loop as long as we can still write new data and have headers to write
+  while ((conn->w.size < LNM_LOOP_BUF_SIZE) &&
+         ((header = res->headers.current) != NULL)) {
+    size_t buf_len = header->name.len + 2 + header->value.len + 1;
+
+    // Here, we also constantly calculate the entire buffer as we assume each
+    // header will be written in one go
+    char buf[buf_len];
+    memcpy(buf, header->name.s, header->name.len);
+    memcpy(&buf[header->name.len + 2], header->value.s, header->value.len);
+    buf[header->name.len] = ':';
+    buf[header->name.len + 1] = ' ';
+    buf[buf_len - 1] = '\n';
+
+    size_t to_write =
+        LNM_MIN(buf_len - res->written, LNM_LOOP_BUF_SIZE - conn->w.size);
+    memcpy(&conn->w.buf[conn->w.size], &buf[res->written], to_write);
+
+    conn->w.size += to_write;
+    res->written += to_write;
+
+    if (res->written == buf_len) {
+      res->written = 0;
+      res->headers.current = res->headers.current->next;
+    }
+  }
+
+  if (res->headers.current == NULL) {
+    ctx->state = ctx->res.body.len > 0 ? lnm_http_loop_state_write_body
+                                       : lnm_http_loop_state_finish;
+  }
+}
+
+void lnm_http_loop_process_write_body(lnm_http_conn *conn) {
+  lnm_http_loop_ctx *ctx = conn->ctx;
+  lnm_http_res *res = &ctx->res;
+
+  size_t to_write =
+      LNM_MIN(res->body.len - res->written, LNM_LOOP_BUF_SIZE - conn->w.size);
+  size_t written;
+
+  switch (res->body.type) {
+  case lnm_http_res_body_type_buf:
+    memcpy(&conn->w.buf[conn->w.size], &res->body.data.buf[res->written],
+           to_write);
+    written = to_write;
+    break;
+  case lnm_http_res_body_type_file:
+    written = fread(&conn->w.buf[conn->w.size], 1, to_write, res->body.data.f);
+
+    if ((written == 0) && (!ferror(res->body.data.f))) {
+      ctx->state = lnm_http_loop_state_finish;
+    }
+    break;
+  case lnm_http_res_body_type_fn:
+    if (res->body.data.fn(&written, &conn->w.buf[conn->w.size], conn,
+                          res->written, to_write) != lnm_err_ok) {
+      ctx->state = lnm_http_loop_state_finish;
+    }
+    break;
+  }
+
+  conn->w.size += written;
+  res->written += written;
+
+  if (res->written == res->body.len) {
+    ctx->state = lnm_http_loop_state_finish;
+  }
+}
+
+void lnm_http_loop_process_finish(lnm_http_conn *conn) {}
+
 void (*process_fns[])(lnm_http_conn *conn) = {
     lnm_http_loop_process_parse_req,
     lnm_http_loop_process_route,
     lnm_http_loop_process_parse_headers,
     lnm_http_loop_process_steps,
+    lnm_http_loop_process_write_status_line,
+    lnm_http_loop_process_write_headers,
+    lnm_http_loop_process_write_body,
+    lnm_http_loop_process_finish,
 };
 
 void lnm_http_loop_process(lnm_http_conn *conn) {
   lnm_http_loop_ctx *ctx = conn->ctx;
 
   lnm_http_loop_state http_loop_state;
-  lnm_loop_state loop_state;
+  lnm_loop_state loop_state = conn->state;
 
   // We stop processing if:
   // - the event loop state has changed, as we need to switch to the other I/O
@@ -143,7 +258,6 @@ void lnm_http_loop_process(lnm_http_conn *conn) {
   // it's waiting for I/O
   do {
     http_loop_state = ctx->state;
-    loop_state = conn->state;
 
     process_fns[http_loop_state](conn);
   } while ((conn->state == loop_state) && (http_loop_state != ctx->state));
diff --git a/lnm/src/http/lnm_http_res.c b/lnm/src/http/lnm_http_res.c
new file mode 100644
index 0000000..adf65f0
--- /dev/null
+++ b/lnm/src/http/lnm_http_res.c
@@ -0,0 +1,64 @@
+#include <string.h>
+
+#include "lnm/http/res.h"
+
+lnm_err lnm_http_res_add_header(lnm_http_res *res, lnm_http_header type,
+                                char *value, bool value_owned) {
+  return lnm_http_res_add_header_len(res, type, value, strlen(value),
+                                     value_owned);
+}
+
+lnm_err lnm_http_res_add_header_len(lnm_http_res *res, lnm_http_header type,
+                                    char *value, size_t value_len,
+                                    bool value_owned) {
+  lnm_http_res_header *header = calloc(1, sizeof(lnm_http_res_header));
+
+  if (header == NULL) {
+    return lnm_err_failed_alloc;
+  }
+
+  lnm_http_res_header **next_ptr = &res->headers.head;
+
+  while ((*next_ptr) != NULL) {
+    next_ptr = &(*next_ptr)->next;
+  }
+
+  *next_ptr = header;
+
+  // Initialize the current pointer to the head of the linked list
+  if (res->headers.current == NULL) {
+    res->headers.current = header;
+  }
+
+  header->name.s = (char *)lnm_http_header_names[type];
+  header->name.len = strlen(lnm_http_header_names[type]);
+  header->name.owned = false;
+
+  header->value.s = value;
+  header->value.len = value_len;
+  header->value.owned = value_owned;
+
+  return lnm_err_ok;
+}
+
+void lnm_http_res_body_set_file(lnm_http_res *res, FILE *f, size_t len,
+                                bool owned) {
+  res->body.data.f = f;
+  res->body.len = len;
+  res->body.owned = owned;
+  res->body.type = lnm_http_res_body_type_file;
+}
+
+void lnm_http_res_body_set_buf(lnm_http_res *res, char *buf, size_t len,
+                               bool owned) {
+  res->body.data.buf = buf;
+  res->body.len = len;
+  res->body.owned = owned;
+  res->body.type = lnm_http_res_body_type_buf;
+}
+
+void lnm_http_res_body_set_fn(lnm_http_res *res, data_fn fn, size_t len) {
+  res->body.data.fn = fn;
+  res->body.len = len;
+  res->body.type = lnm_http_res_body_type_fn;
+}